U.S. patent number 11,381,819 [Application Number 16/918,741] was granted by the patent office on 2022-07-05 for chroma delta quantization parameter (qp) in video coding.
This patent grant is currently assigned to QUALCOMM Incorporated. The grantee listed for this patent is QUALCOMM Incorporated. Invention is credited to Yung-Hsuan Chao, Wei-Jung Chien, Muhammed Zeyd Coban, Yu Han, Marta Karczewicz, Alican Nalci, Geert Van der Auwera.
United States Patent |
11,381,819 |
Han , et al. |
July 5, 2022 |
Chroma delta quantization parameter (QP) in video coding
Abstract
Examples of block-level signaling of quantization parameter
offsets is described. Such block-level signaling of quantization
parameter offsets provides block level flexibility to determine a
more precise chroma quantization parameter (QP) for a chroma block.
With the block-level quantization parameter offset signaling
described in this disclosure, there is more flexibility in defining
the chroma QP, resulting in more accurate determination of chroma
QP on a chroma block-by-chroma block basis.
Inventors: |
Han; Yu (San Diego, CA), Van
der Auwera; Geert (Del Mar, CA), Coban; Muhammed Zeyd
(Carlsbad, CA), Chien; Wei-Jung (San Diego, CA), Chao;
Yung-Hsuan (San Diego, CA), Nalci; Alican (San Diego,
CA), Karczewicz; Marta (San Diego, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
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Assignee: |
QUALCOMM Incorporated (San
Diego, CA)
|
Family
ID: |
1000006415305 |
Appl.
No.: |
16/918,741 |
Filed: |
July 1, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210006792 A1 |
Jan 7, 2021 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62871028 |
Jul 5, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N
19/463 (20141101); H04N 19/186 (20141101); H04N
19/96 (20141101); H04N 19/124 (20141101); H04N
19/176 (20141101) |
Current International
Class: |
H04N
19/124 (20140101); H04N 19/176 (20140101); H04N
19/96 (20140101); H04N 19/463 (20140101); H04N
19/186 (20140101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3026657 |
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Jan 2018 |
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2017206826 |
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|
Primary Examiner: Jean Baptiste; Jerry T
Attorney, Agent or Firm: Shumaker & Sieffert, P.A.
Parent Case Text
This application claims the benefit of U.S. Provisional Application
No. 62/871,028, filed Jul. 5, 2019, the entire contents of which
are hereby incorporated by reference.
Claims
What is claimed is:
1. A method of decoding video data, the method comprising:
determining a quantization parameter predictor for a first chroma
block of a first chroma component and a second chroma block of a
second chroma component of the video data based on a quantization
parameter for a corresponding luma block; determining a first block
level quantization parameter offset for the first chroma block from
an index into a first list of quantization parameter offsets for
the first chroma component; determining a first quantization
parameter for the first chroma block based on the first block level
quantization parameter offset and the quantization parameter
predictor; determining a first residual block based on the first
quantization parameter; reconstructing the first chroma block based
on the first residual block; determining a second block level
quantization parameter offset, for the second chroma block, from
the index into a second list of quantization parameter offsets for
the second chroma component, wherein the index into the first list
of quantization parameter offsets is same as the index into the
second list of quantization parameter offsets; determining a second
quantization parameter for the second chroma block based on the
second block level quantization parameter offset and the
quantization parameter predictor; determining a second residual
block based on the second quantization parameter; and
reconstructing the second chroma block based on the second residual
block.
2. The method of claim 1, wherein determining the first block level
quantization parameter offset comprises: constructing the first
list of quantization parameter offsets; receiving the index into
the first list of quantization parameter offsets; and determining
the first block level quantization parameter offset based on the
index into the first list of quantization parameter offsets.
3. The method of claim 1, further comprising: receiving at least
one of a first quantization parameter offset for the first chroma
component in a picture parameter set or a second quantization
parameter offset for the first chroma component in a slice
parameter set, wherein determining the first quantization parameter
for the first chroma block comprises determining the first
quantization parameter for the first chroma block based on the
first block level quantization parameter offset, at least one of
the first quantization parameter offset or the second quantization
parameter offset, and the quantization parameter predictor.
4. The method of claim 1, further comprising: receiving a syntax
element indicating that use of block level quantization parameter
offsets is enabled, wherein determining the first block level
quantization parameter offset for the first chroma block comprises
determining the first block level quantization parameter offset
based on the syntax element indicating that the use of block level
quantization parameter offsets is enabled.
5. The method of claim 1, wherein the first block level
quantization parameter offset is different for at least one other
chroma block in a same slice or picture as the first chroma block
and is determined on a chroma block-by-chroma block basis.
6. The method of claim 1, wherein determining the first residual
block based on the first quantization parameter comprises:
inverse-quantizing a plurality of coefficient values based on the
first quantization parameter to generate inverse-quantized
coefficient values; and inverse-transforming the inverse-quantized
coefficient values to generate the first residual block.
7. The method of claim 1, wherein reconstructing the first chroma
block comprises: determining a prediction block for the first
chroma block; and adding the first residual block to the prediction
block to reconstruct the first chroma block.
8. A device for decoding video data, the device comprising: memory
configured to store a quantization parameter for a corresponding
luma block of a first chroma block of a first chroma component and
a second chroma block of a second chroma component of the video
data; and processing circuitry coupled to the memory and configured
to: determine a quantization parameter predictor for the first
chroma block and the second chroma block of the video data based on
the quantization parameter for the corresponding luma block;
determine a first block level quantization parameter offset, for
the first chroma block, from an index into a first list of
quantization parameter offsets for the first chroma component;
determine a first quantization parameter for the first chroma block
based on the first block level quantization parameter offset and
the quantization parameter predictor; determine a first residual
block based on the first quantization parameter; reconstruct the
first chroma block based on the first residual block; determine a
second block level quantization parameter offset, for the second
chroma block, from the index into a second list of quantization
parameter offsets for the second chroma component, wherein the
index into the first list of quantization parameter offsets is same
as the index into the second list of quantization parameter
offsets; determine a second quantization parameter for the second
chroma block based on the second block level quantization parameter
offset and the quantization parameter predictor; determine a second
residual block based on the second quantization parameter; and
reconstruct the second chroma block based on the second residual
block.
9. The device of claim 8, wherein to determine the first block
level quantization parameter offset, the processing circuitry is
configured to: construct the first list of quantization parameter
offsets; receive the index into the first list of quantization
parameter offsets; and determine the first block level quantization
parameter offset based on the index into the first list of
quantization parameter offsets.
10. The device of claim 8, wherein the processing circuitry is
configured to: receive at least one of a first quantization
parameter offset for the first chroma component in a picture
parameter set or a second quantization parameter offset for the
first chroma component in a slice parameter set, wherein to
determine the first quantization parameter for the first chroma
block, the processing circuitry is configured to determine the
first quantization parameter for the first chroma block based on
the first block level quantization parameter offset, at least one
of the first quantization parameter offset or the second
quantization parameter offset, and the quantization parameter
predictor.
11. The device of claim 8, wherein the processing circuitry is
configured to: receive a syntax element indicating that use of
block level quantization parameter offsets is enabled offset is to
be used for determining the block level quantization parameter
offset for the chroma block, wherein to determine the first block
level quantization parameter offset for the first chroma block, the
processing circuitry is configured to determine the first block
level quantization parameter offset based on the syntax element
indicating that the use of block level quantization parameter
offsets is enabled.
12. The device of claim 8, wherein the first block level
quantization parameter offset is different for at least one other
chroma block in a same slice or picture as the first chroma block
and is determined on a chroma block-by-chroma block basis.
13. The device of claim 8, wherein to determine the first residual
block based on the first quantization parameter, the processing
circuitry is configured to: inverse-quantize a plurality of
coefficient values based on the first quantization parameter to
generate inverse-quantized coefficient values; and
inverse-transform the inverse-quantized coefficient values to
generate the first residual block.
14. The device of claim 8, wherein to reconstruct the first chroma
block, the processing circuitry is configured to: determine a
prediction block for the first chroma block; and add the first
residual block to the prediction block to reconstruct the first
chroma block.
15. The device of claim 8, comprising a display configured to
display decoded video data.
16. The device of claim 8, wherein the device comprises one of a
camera, a computer, a wireless communication device, a broadcast
receiver device, or a set-top box.
17. A non-transitory computer-readable storage medium storing
instructions thereon that when executed cause one or more
processors of a device for decoding video data to: determine a
quantization parameter predictor for a first chroma block of a
first chroma component and a second chroma block of a second chroma
component of the video data based on a quantization parameter for a
corresponding luma block; determine a first block level
quantization parameter offset, for the first chroma block, from an
index into a first list of quantization parameter offsets for the
first chroma component; determine a first quantization parameter
for the first chroma block based on the first block level
quantization parameter offset and the quantization parameter
predictor; determine a first residual block based on the first
quantization parameter; reconstruct the first chroma block based on
the first residual block; determine a second block level
quantization parameter offset, for the second chroma block, from
the index into a second list of quantization parameter offsets for
the second chroma component, wherein the index into the first list
of quantization parameter offsets is same as the index into the
second list of quantization parameter offsets; determine a second
quantization parameter for the second chroma block based on the
second block level quantization parameter offset and the
quantization parameter predictor; determine a second residual block
based on the second quantization parameter; and reconstruct the
second chroma block based on the second residual block.
18. The non-transitory computer-readable storage medium of claim
17, wherein the instructions that cause the one or more processors
to determine the first block level quantization parameter offset
comprise instructions that cause the one or more processors to:
construct the first list of quantization parameter offsets; receive
the index into the first list of quantization parameter offsets;
and determine the first block level quantization parameter offset
based on the index into the first list of quantization parameter
offsets.
19. The non-transitory computer-readable storage medium of claim
17, further comprising instructions that cause the one or more
processors to: receive at least one of a first quantization
parameter offset for the first chroma component in a picture
parameter set or a second quantization parameter offset for the
first chroma component in a slice parameter set, wherein the
instructions that cause the one or more processors to determine the
first quantization parameter for the first chroma block comprise
instructions that cause the one or more processors to determine the
first quantization parameter for the first chroma block based on
the first block level quantization parameter offset, at least one
of the first quantization parameter offset or the second
quantization parameter offset, and the quantization parameter
predictor.
20. A device for decoding video data, the device comprising: means
for determining a quantization parameter predictor for a first
chroma block of a first chroma component and a second chroma block
of a second chroma component of the video data based on a
quantization parameter for a corresponding luma block; means for
determining a first block level quantization parameter offset for
the chroma block, from an index into a first list of quantization
parameter offsets for the first chroma component; means for
determining a first quantization parameter for the first chroma
block based on the first block level quantization parameter offset
and the quantization parameter predictor; means for determining a
first residual block based on the first quantization parameter;
means for reconstructing the first chroma block based on the first
residual block; means for determining a second block level
quantization parameter offset, for the second chroma block, from
the index into a second list of quantization parameter offsets for
the second chroma component, wherein the index into the first list
of quantization parameter offsets is same as the index into the
second list of quantization parameter offsets; means for
determining a second quantization parameter for the second chroma
block based on the second block level quantization parameter offset
and the quantization parameter predictor; means for determining a
second residual block based on the second quantization parameter;
and means for reconstructing the second chroma block based on the
second residual block.
21. The device of claim 20, wherein the means for determining the
first block level quantization parameter offset comprises: means
for constructing the first list of quantization parameter offsets;
means for receiving the index into the first list of quantization
parameter offsets; and means for determining the first block level
quantization parameter offset based on the index into the first
list of quantization parameter offsets.
22. The device of claim 20, further comprising: means for receiving
at least one of a first quantization parameter offset for the first
chroma component in a picture parameter set or a second
quantization parameter offset for the first chroma component in a
slice parameter set, wherein the means for determining the first
quantization parameter for the first chroma block comprises means
for determining the first quantization parameter for the first
chroma block based on the first block level quantization parameter
offset, at least one of the first quantization parameter offset or
the second quantization parameter offset, and the quantization
parameter predictor.
23. The device of claim 20, further comprising: means for receiving
a syntax element indicating that use of block level quantization
parameter offsets is enabled, wherein the means for determining the
first block level quantization parameter offset for the first
chroma block comprises means for determining the first block level
quantization parameter offset based on the syntax element
indicating that the use of block level quantization parameter
offsets is enabled.
24. A method of encoding video data, the method comprising:
determining a quantization parameter predictor for a first chroma
block of a first chroma component and a second chroma block of a
seconc chroma component of the video data based on a quantization
parameter for a corresponding luma block; determining a first block
level quantization parameter offset for the chroma block wherein an
index into a first list of quantization parameter offsets for the
first chroma component identifies the first block level
quantization parameter offset; determining a first quantization
parameter for the first chroma block based on the first block level
quantization parameter offset and the quantization parameter
predictor; quantizing coefficient values for a first residual block
based on the first quantization parameter for the first chroma
block; signaling information indicative of the quantized
coefficient values for the first chroma block; determining a second
block level quantization parameter offset, for the second chroma
block, wherien an index into a second list of quantization
parameter offsets for the second chroma component identifies the
second block level quantization parameter offset and is same as the
index into the first list of quantization parameter offsets;
determining a second quantization parameter for the second chroma
block based on the second block level quantization parameter offset
and the quantization parameter predictor; quantizing coefficient
values for a second residual block based on the second quantization
parameter; and signaling information indicative of the quantized
coefficient values for the second residual block.
25. The method of claim 24, further comprising: constructing the
first list of quantization parameter offsets; determining the index
into the first list of quantization parameter offsets for the first
block level quantization parameter offset; and signaling
information indicative of the index.
26. The method of claim 24, further comprising: signaling at least
one of a first quantization parameter offset for the first chroma
component in a picture parameter set or a second quantization
parameter offset for the first chroma component in a slice
parameter set, wherein determining the first quantization parameter
for the first chroma block comprises determining the first
quantization parameter for the first chroma block based on the
first block level quantization parameter offset, at least one of
the first quantization parameter offset or the second quantization
parameter offset, and the quantization parameter predictor.
27. The method of claim 24, further comprising: signaling a syntax
element indicating that the use of block level quantization
parameter offsets is enabled.
28. A device for encoding video data, the device comprising: memory
configured to store a quantization parameter for a corresponding
luma block of a first chroma block of a first chroma component and
a second chroma block of a second chroma component of the video
data; and processing circuitry coupled to the memory and configured
to: determine a quantization parameter predictor for the first
chroma block and the second chroma block of the video data based on
the quantization parameter for the corresponding luma block;
determine a first block level quantization parameter offset for the
first chroma block, wherein an index into a first list of
quantization parameter offsets for the first chroma component
identifies the first block level quantization parameter offset;
determine a first quantization parameter for the first chroma block
based on the first block level quantization parameter offset and
the quantization parameter predictor; quantize coefficient values
for a first residual block based on the first quantization
parameter for the first chroma block; signal information indicative
of the quantized coefficient values for the first chroma block;
determine a second block level quantization parameter offset, for
the second chroma block, wherien an index into a second list of
quantization parameter offsets for the second chroma component
identifies the second block level quantization parameter offset and
is same as the index into the first list of quantization parameter
offsets; determine a second quantization parameter for the second
chroma block based on the second block level quantization parameter
offset and the same quantization parameter predictor; quantize
coefficient values for a second residual block based on the second
quantization parameter; and signal information indicative of the
quantized coefficient values for the second residual block.
29. The device of claim 28, wherein the processing circuitry is
configured to: construct the first list of quantization parameter
offsets; determine the index into the first list of quantization
parameter offsets for the first block level quantization parameter
offset; and signal information indicative of the index.
30. The device of claim 28, wherein the processing circuitry is
configured to: signal at least one of a first quantization
parameter offset for the first chroma component in a picture
parameter set or a second quantization parameter offset for the
first chroma component in a slice parameter set, wherein to
determine the first quantization parameter for the first chroma
block, the processing circuitry is configured to determine the
first quantization parameter for the first chroma block based on
the first block level quantization parameter offset, at least one
of the first quantization parameter offset or the second
quantization parameter offset, and the quantization parameter
predictor.
31. The device of claim 28, wherein the processing circuitry is
configured to: signal a syntax element indicating that the use of
block level quantization parameter offsets is enabled.
Description
TECHNICAL FIELD
This disclosure relates to video encoding and video decoding.
BACKGROUND
Digital video capabilities can be incorporated into a wide range of
devices, including digital televisions, digital direct broadcast
systems, wireless broadcast systems, personal digital assistants
(PDAs), laptop or desktop computers, tablet computers, e-book
readers, digital cameras, digital recording devices, digital media
players, video gaming devices, video game consoles, cellular or
satellite radio telephones, so-called "smart phones," video
teleconferencing devices, video streaming devices, and the like.
Digital video devices implement video coding techniques, such as
those described in the standards defined by MPEG-2, MPEG-4, ITU-T
H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC),
ITU-T H.265/High Efficiency Video Coding (HEVC), and extensions of
such standards. The video devices may transmit, receive, encode,
decode, and/or store digital video information more efficiently by
implementing such video coding techniques.
Video coding techniques include spatial (intra-picture) prediction
and/or temporal (inter-picture) prediction to reduce or remove
redundancy inherent in video sequences. For block-based video
coding, a video slice (e.g., a video picture or a portion of a
video picture) may be partitioned into video blocks, which may also
be referred to as coding tree units (CTUs), coding units (CUs)
and/or coding nodes. Video blocks in an intra-coded (I) slice of a
picture are encoded using spatial prediction with respect to
reference samples in neighboring blocks in the same picture. Video
blocks in an inter-coded (P or B) slice of a picture may use
spatial prediction with respect to reference samples in neighboring
blocks in the same picture or temporal prediction with respect to
reference samples in other reference pictures. Pictures may be
referred to as frames, and reference pictures may be referred to as
reference frames.
SUMMARY
In general, this disclosure describes techniques for determining
chroma quantization parameter (QP). The techniques may be applied
to any of the existing video codecs, such as HEVC (High Efficiency
Video Coding), VVC (Versatile Video Coding), or be an efficient
coding tool in any future video coding standards.
In video coding, a chroma QP indicates an amount of quantization
that a video encoder applies to coefficient values of a residual
block and an amount of inverse-quantization that a video decoder
applies to quantized coefficient values to generate the residual
block. In some examples, rather than a video encoder signaling the
chroma QP, a video decoder may utilize a QP predictor, which may be
based on a luma QP of a corresponding luma block to the chroma
block, and one or more quantization parameter offsets to determine
the chroma QP.
This disclosure describes example techniques of block-level
signaling of quantization parameter offsets. Such block-level
signaling of quantization parameter offsets provides block level
flexibility to determine a more precise chroma QP for a chroma
block. For instance, some techniques relied on quantization
parameter offsets that are signaled at a picture level or slice
level, so that the quantization parameter offsets were the same for
each chroma block in the picture or slice. Such high level
signaling (e.g., at picture and/or slice level) limits granularity
in defining the chroma QP for a chroma block. With the block-level
quantization parameter offset signaling described in this
disclosure, there is more flexibility in defining the chroma QP,
resulting in more accurate determination of chroma QP on a chroma
block-by-chroma block basis.
In this way, the example techniques provide technical solutions to
a technical problem by providing signaling that increases
flexibility to more accurately define the chroma QP. The example
techniques described in more detail provide a practical application
to video coding, such as a way in which to determine the chroma QP
that is more accurate, resulting in better video coding, as
compared to other techniques that rely on high level signaling such
as picture level or slice level signaling to define the offsets for
determining the chroma QP.
In one example, the disclosure describes a method of decoding video
data, the method comprising determining a quantization parameter
predictor for a chroma block of the video data based on a
quantization parameter for a corresponding luma block, determining
a block level quantization parameter offset for the chroma block,
determining a quantization parameter for the chroma block based on
the block level quantization parameter offset and the quantization
parameter predictor, determining a residual block based on the
quantization parameter, and reconstructing the chroma block based
on the residual block.
In one example, the disclosure describes a device for decoding
video data, the device comprising memory configured to store a
quantization parameter for a corresponding luma block of a chroma
block of the video data and processing circuitry coupled to the
memory and configured to determine a quantization parameter
predictor for the chroma block of the video data based on the
quantization parameter for the corresponding luma block, determine
a block level quantization parameter offset for the chroma block,
determine a quantization parameter for the chroma block based on
the block level quantization parameter offset and the quantization
parameter predictor, determine a residual block based on the
quantization parameter, and reconstruct the chroma block based on
the residual block.
In one example, the disclosure describes a computer-readable
storage medium storing instructions thereon that when executed
cause one or more processors of a device for decoding video data to
determine a quantization parameter predictor for a chroma block of
the video data based on a quantization parameter for a
corresponding luma block, determine a block level quantization
parameter offset for the chroma block, determine a quantization
parameter for the chroma block based on the block level
quantization parameter offset and the quantization parameter
predictor, determine a residual block based on the quantization
parameter, and reconstruct the chroma block based on the residual
block.
In one example, the disclosure describes a device for decoding
video data, the device comprising means for determining a
quantization parameter predictor for a chroma block of the video
data based on a quantization parameter for a corresponding luma
block, means for determining a block level quantization parameter
offset for the chroma block, means for determining a quantization
parameter for the chroma block based on the block level
quantization parameter offset and the quantization parameter
predictor, means for determining a residual block based on the
quantization parameter, and means for reconstructing the chroma
block based on the residual block.
In one example, the disclosure describes a method of encoding video
data, the method comprising determining a quantization parameter
predictor for a chroma block of the video data based on a
quantization parameter for a corresponding luma block, determining
a block level quantization parameter offset for the chroma block,
determining a quantization parameter for the chroma block based on
the block level quantization parameter offset and the quantization
parameter predictor, quantizing coefficient values for a residual
block based on the determined quantization parameter for the chroma
block, and signaling information indicative of the quantized
coefficient values.
In one example, the disclosure describes a device for encoding
video data, the device comprising memory configured to store a
quantization parameter for a corresponding luma block of a chroma
block of the video data and processing circuitry coupled to the
memory and configured to determine a quantization parameter
predictor for a chroma block of the video data based on a
quantization parameter for a corresponding luma block, determine a
block level quantization parameter offset for the chroma block,
determine a quantization parameter for the chroma block based on
the block level quantization parameter offset and the quantization
parameter predictor, quantize coefficient values for a residual
block based on the determined quantization parameter for the chroma
block, and signal information indicative of the quantized
coefficient values.
The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description,
drawings, and claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating an example video encoding
and decoding system that may perform the techniques of this
disclosure.
FIGS. 2A and 2B are conceptual diagrams illustrating an example
quadtree binary tree (QTBT) structure, and a corresponding coding
tree unit (CTU).
FIG. 3 is a block diagram illustrating an example video encoder
that may perform the techniques of this disclosure.
FIG. 4 is a block diagram illustrating an example video decoder
that may perform the techniques of this disclosure.
FIG. 5 is a conceptual diagram illustrating an example of a chroma
coding unit (CU) and its corresponding luma CUs in separate
tree.
FIG. 6 is a flowchart illustrating an example method for encoding a
current block of video data.
FIG. 7 is a flowchart illustrating an example method for decoding a
current block of video data.
DETAILED DESCRIPTION
In video coding, a video encoder determines a prediction block for
a current block being encoded and determines a residual block
indicative of difference between the prediction block and the
current block. The video encoder may perform a transform that
transforms the residual values to transform coefficients. The
transform may be skipped in some cases. After transform (or where
transform is skipped), the video encoder performs a quantization of
the coefficients. The video encoder signals the quantized
coefficients to the video decoder which performs the reciprocal
operations as the video encoder to generate the residual block.
Video decoder utilizes the same techniques as the video encoder to
determine the prediction block and adds the residual block to the
prediction block to reconstruct the current block.
The video coding process is performed on luma and chroma
components. In other words, the current block includes a luma block
and one or more chroma blocks. The chroma block(s) may be
subsampled relative to the luma block based on the particular color
format.
A quantization parameter determines how much quantization the video
encoder applies and amount of inverse quantization the video
decoder applies. In some examples, rather than signaling the
quantization parameter for a chroma block, the quantization
parameter for a luma block corresponding to the chroma block may be
used to determine a quantization parameter predictor for the
quantization parameter for the chroma block. For example, the
quantization parameter for the luma block is the quantization
parameter predictor, but other ways to determine the quantization
parameter predictor based on the quantization parameter for the
luma block are possible (e.g., such as average of quantization
parameters of neighboring luma blocks). In such examples, for a
chroma block, the video encoder may signal offsets that the video
decoder adds to the quantization parameter predictor.
In some techniques, the offsets that the video encoder signals are
offsets that are constant for the entire picture or entire slice of
the current block. For example, the offset may be pps_cb_qp_offset
for the Cb chroma block or pps_cr_qp_offset for the Cr chroma
block. These example offsets are at a picture level (e.g.,
applicable to blocks in the picture). Another example is the
slice_cb_qp_offset for the Cb chroma block or slice_cr_qp_offset
for the Cr chroma block. These example offsets are at a slice level
(e.g., applicable to blocks in the slice). Accordingly, if the
Qp.sub.Y (e.g., QP for luma) is the quantization parameter
predictor, then in some techniques, the Qp.sub.CR (quantization
parameter for Cr chroma block) is
Qp.sub.Y+pps_cb_qp_offset+slice_cb_qp_offset, clipped to within a
specified range. The Qp.sub.CB (quantization parameter for Cb
chroma block) is Qp.sub.Y+pps_cr_qp_offset+slice_cr_qp_offset,
clipped to within a specified range. It should be understood that
Qp.sub.Y being the quantization parameter predictor is merely one
example and should not be considered limiting. In some examples,
the quantization parameter predictor may be determined from
Qp.sub.Y, and may not explicitly be Qp.sub.Y.
There may be problems with such techniques. The picture level and
slice level offsets (e.g., pps_cb or cr_qp_offset and slice_cb or
cr_qp_offset, respectively) may not provide sufficient flexibility
to allow the video decoder to accurately determine the quantization
parameter for a chroma block. For example, if the actual chroma
block quantization parameter for the Cb chroma block is different
than Qp.sub.Y+pps_cb_qp_offset+slice_cb_qp_offset, there may not be
a way for the video encoder to further refine the quantization
parameter for the Cb chroma block because the quantization
parameter for the Cb chroma block may be limited to three factors:
Qp.sub.Y, pps_cb_qp_offset, and slice_cb_qp_offset.
This disclosure describes block level signaling of offset that the
video encoder or video decoder can add to a quantization parameter
predictor to determine a quantization parameter for a chroma block.
As one example, the video encoder and the video decoder each
construct a list of quantization parameter offsets. The video
encoder signals an index into the list of quantization parameter
offsets, and the video decoder determines the block level
quantization parameter offset based on the index into the list of
quantization parameter offsets and adds the offset to the
quantization parameter predictor.
For example, assume that CuQpOffsetCb is the block level
quantization parameter offset that the video decoder determines
based on an index into the list of quantization parameter offsets
for the Cb chroma block, and CuQpOffsetCr is the block level
quantization parameter offset that the video decoder determines
based on the index into the list of quantization parameter offsets
for the Cr chroma block. For such examples, the quantization
parameter for the Cb chroma block may be
Qp.sub.Y+pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffsetCb, and the
quantization parameter for the Cr chroma block may be
Qp.sub.Y+pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffsetCr. The same
may apply for joint Cb Cr blocks.
In this way, CuQpOffsetCb and CuQpOffsetCb provide block level
flexibility for determining the quantization parameter for Cb and
Cr chroma blocks. For instance, without CuQpOffsetCb and
CuQpOffsetCb, the quantization parameter for Cb and Cr chroma
blocks would be limited by the quantization parameter predictor and
quantization parameter offsets signaled at picture level or slice
level, and there would not be a way in which to define the
quantization parameter based on block level quantization parameter
offsets. With the example techniques described in this disclosure,
the video encoder can signal information to define block level
quantization parameter offsets, rather than being limited to
picture level or slice level signaling of quantization parameter
offsets.
For example, the block level quantization parameter offset for two
chroma blocks (e.g., two Cb chroma blocks or two Cr chroma blocks)
in the same picture or slice may be different, and the block level
quantization parameter offsets may be determined on a chroma
block-by-chroma block basis. The pps_cb_qp_offset and
pps_cr_qp_offset are picture level offset, so that two Cb chroma
blocks or two Cr chroma blocks in the same picture have the same
pps_cb_qp_offset or the same pps_cr_qp_offset, respectively. The
slice_cb_qp_offset and slice_cr_qp_offset are slice level offsets,
so that two Cb chroma blocks or two Cr chroma blocks in the same
slice have the same slice_cb_qp_offset or slice_cr_qp_offset,
respectively.
FIG. 1 is a block diagram illustrating an example video encoding
and decoding system 100 that may perform the techniques of this
disclosure. The techniques of this disclosure are generally
directed to coding (encoding and/or decoding) video data. In
general, video data includes any data for processing a video. Thus,
video data may include raw, unencoded video, encoded video, decoded
(e.g., reconstructed) video, and video metadata, such as signaling
data.
As shown in FIG. 1, system 100 includes a source device 102 that
provides encoded video data to be decoded and displayed by a
destination device 116, in this example. In particular, source
device 102 provides the video data to destination device 116 via a
computer-readable medium 110. Source device 102 and destination
device 116 may comprise any of a wide range of devices, including
desktop computers, notebook (i.e., laptop) computers, tablet
computers, set-top boxes, telephone handsets such as smartphones,
televisions, cameras, display devices, digital media players, video
gaming consoles, video streaming device, broadcast receiver
devices, or the like. In some cases, source device 102 and
destination device 116 may be equipped for wireless communication,
and thus may be referred to as wireless communication devices.
In the example of FIG. 1, source device 102 includes video source
104, memory 106, video encoder 200, and output interface 108.
Destination device 116 includes input interface 122, video decoder
300, memory 120, and display device 118. In accordance with this
disclosure, video encoder 200 of source device 102 and video
decoder 300 of destination device 116 may be configured to apply
the techniques for signaling and parsing chroma delta quantization
parameter (QP). Thus, source device 102 represents an example of a
video encoding device, while destination device 116 represents an
example of a video decoding device. In other examples, a source
device and a destination device may include other components or
arrangements. For example, source device 102 may receive video data
from an external video source, such as an external camera.
Likewise, destination device 116 may interface with an external
display device, rather than including an integrated display
device.
System 100 as shown in FIG. 1 is merely one example. In general,
any digital video encoding and/or decoding device may perform
techniques for signaling and parsing chroma delta QP. Source device
102 and destination device 116 are merely examples of such coding
devices in which source device 102 generates coded video data for
transmission to destination device 116. This disclosure refers to a
"coding" device as a device that performs coding (encoding and/or
decoding) of data. Thus, video encoder 200 and video decoder 300
represent examples of coding devices, in particular, a video
encoder and a video decoder, respectively. In some examples,
devices 102, 116 may operate in a substantially symmetrical manner
such that each of devices 102, 116 include video encoding and
decoding components. Hence, system 100 may support one-way or
two-way video transmission between video devices 102, 116, e.g.,
for video streaming, video playback, video broadcasting, or video
telephony.
In general, video source 104 represents a source of video data
(i.e., raw, unencoded video data) and provides a sequential series
of pictures (also referred to as "frames") of the video data to
video encoder 200, which encodes data for the pictures. Video
source 104 of source device 102 may include a video capture device,
such as a video camera, a video archive containing previously
captured raw video, and/or a video feed interface to receive video
from a video content provider. As a further alternative, video
source 104 may generate computer graphics-based data as the source
video, or a combination of live video, archived video, and
computer-generated video. In each case, video encoder 200 encodes
the captured, pre-captured, or computer-generated video data. Video
encoder 200 may rearrange the pictures from the received order
(sometimes referred to as "display order") into a coding order for
coding. Video encoder 200 may generate a bitstream including
encoded video data. Source device 102 may then output the encoded
video data via output interface 108 onto computer-readable medium
110 for reception and/or retrieval by, e.g., input interface 122 of
destination device 116.
Memory 106 of source device 102 and memory 120 of destination
device 116 represent general purpose memories. In some examples,
memories 106, 120 may store raw video data, e.g., raw video from
video source 104 and raw, decoded video data from video decoder
300. Additionally or alternatively, memories 106, 120 may store
software instructions executable by, e.g., video encoder 200 and
video decoder 300, respectively. Although shown separately from
video encoder 200 and video decoder 300 in this example, it should
be understood that video encoder 200 and video decoder 300 may also
include internal memories for functionally similar or equivalent
purposes. Furthermore, memories 106, 120 may store encoded video
data, e.g., output from video encoder 200 and input to video
decoder 300. In some examples, portions of memories 106, 120 may be
allocated as one or more video buffers, e.g., to store raw,
decoded, and/or encoded video data.
Computer-readable medium 110 may represent any type of medium or
device capable of transporting the encoded video data from source
device 102 to destination device 116. In one example,
computer-readable medium 110 represents a communication medium to
enable source device 102 to transmit encoded video data directly to
destination device 116 in real-time, e.g., via a radio frequency
network or computer-based network. Output interface 108 may
modulate a transmission signal including the encoded video data,
and input interface 122 may demodulate the received transmission
signal, according to a communication standard, such as a wireless
communication protocol. The communication medium may comprise any
wireless or wired communication medium, such as a radio frequency
(RF) spectrum or one or more physical transmission lines. The
communication medium may form part of a packet-based network, such
as a local area network, a wide-area network, or a global network
such as the Internet. The communication medium may include routers,
switches, base stations, or any other equipment that may be useful
to facilitate communication from source device 102 to destination
device 116.
In some examples, source device 102 may output encoded data from
output interface 108 to storage device 112. Similarly, destination
device 116 may access encoded data from storage device 112 via
input interface 122. Storage device 112 may include any of a
variety of distributed or locally accessed data storage media such
as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory,
volatile or non-volatile memory, or any other suitable digital
storage media for storing encoded video data.
In some examples, source device 102 may output encoded video data
to file server 114 or another intermediate storage device that may
store the encoded video data generated by source device 102.
Destination device 116 may access stored video data from file
server 114 via streaming or download.
File server 114 may be any type of server device capable of storing
encoded video data and transmitting that encoded video data to the
destination device 116. File server 114 may represent a web server
(e.g., for a website), a server configured to provide a file
transfer protocol service (such as File Transfer Protocol (FTP) or
File Delivery over Unidirectional Transport (FLUTE) protocol), a
content delivery network (CDN) device, a hypertext transfer
protocol (HTTP) server, a Multimedia Broadcast Multicast Service
(MBMS) or Enhanced MBMS (eMBMS) server, and/or a network attached
storage (NAS) device. File server 114 may, additionally or
alternatively, implement one or more HTTP streaming protocols, such
as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming
(HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming,
or the like.
Destination device 116 may access encoded video data from file
server 114 through any standard data connection, including an
Internet connection. This may include a wireless channel (e.g., a
Wi-Fi connection), a wired connection (e.g., digital subscriber
line (DSL), cable modem, etc.), or a combination of both that is
suitable for accessing encoded video data stored on file server
114. Input interface 122 may be configured to operate according to
any one or more of the various protocols discussed above for
retrieving or receiving media data from file server 114, or other
such protocols for retrieving media data.
Output interface 108 and input interface 122 may represent wireless
transmitters/receivers, modems, wired networking components (e.g.,
Ethernet cards), wireless communication components that operate
according to any of a variety of IEEE 802.11 standards, or other
physical components. In examples where output interface 108 and
input interface 122 comprise wireless components, output interface
108 and input interface 122 may be configured to transfer data,
such as encoded video data, according to a cellular communication
standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced,
5G, or the like. In some examples where output interface 108
comprises a wireless transmitter, output interface 108 and input
interface 122 may be configured to transfer data, such as encoded
video data, according to other wireless standards, such as an IEEE
802.11 specification, an IEEE 802.15 specification (e.g.,
ZigBee.TM.), a Bluetooth.TM. standard, or the like. In some
examples, source device 102 and/or destination device 116 may
include respective system-on-a-chip (SoC) devices. For example,
source device 102 may include an SoC device to perform the
functionality attributed to video encoder 200 and/or output
interface 108, and destination device 116 may include an SoC device
to perform the functionality attributed to video decoder 300 and/or
input interface 122.
The techniques of this disclosure may be applied to video coding in
support of any of a variety of multimedia applications, such as
over-the-air television broadcasts, cable television transmissions,
satellite television transmissions, Internet streaming video
transmissions, such as dynamic adaptive streaming over HTTP (DASH),
digital video that is encoded onto a data storage medium, decoding
of digital video stored on a data storage medium, or other
applications.
Input interface 122 of destination device 116 receives an encoded
video bitstream from computer-readable medium 110 (e.g., storage
device 112, file server 114, or the like). The encoded video
bitstream may include signaling information defined by video
encoder 200, which is also used by video decoder 300, such as
syntax elements having values that describe characteristics and/or
processing of video blocks or other coded units (e.g., slices,
pictures, groups of pictures, sequences, or the like). Display
device 118 displays decoded pictures of the decoded video data to a
user. Display device 118 may represent any of a variety of display
devices such as a cathode ray tube (CRT), a liquid crystal display
(LCD), a plasma display, an organic light emitting diode (OLED)
display, or another type of display device.
Although not shown in FIG. 1, in some examples, video encoder 200
and video decoder 300 may each be integrated with an audio encoder
and/or audio decoder, and may include appropriate MUX-DEMUX units,
or other hardware and/or software, to handle multiplexed streams
including both audio and video in a common data stream. If
applicable, MUX-DEMUX units may conform to the ITU H.223
multiplexer protocol, or other protocols such as the user datagram
protocol (UDP).
Video encoder 200 and video decoder 300 each may be implemented as
any of a variety of suitable encoder and/or decoder circuitry, such
as one or more microprocessors, digital signal processors (DSPs),
application specific integrated circuits (ASICs), field
programmable gate arrays (FPGAs), discrete logic, software,
hardware, firmware or any combinations thereof. When the techniques
are implemented partially in software, a device may store
instructions for the software in a suitable, non-transitory
computer-readable medium and execute the instructions in hardware
using one or more processors to perform the techniques of this
disclosure. Each of video encoder 200 and video decoder 300 may be
included in one or more encoders or decoders, either of which may
be integrated as part of a combined encoder/decoder (CODEC) in a
respective device. A device including video encoder 200 and/or
video decoder 300 may comprise an integrated circuit, a
microprocessor, and/or a wireless communication device, such as a
cellular telephone.
Video encoder 200 and video decoder 300 may operate according to a
video coding standard, such as ITU-T H.265, also referred to as
High Efficiency Video Coding (HEVC) or extensions thereto, such as
the multi-view and/or scalable video coding extensions. Description
of HEVC is available at G. J. Sullivan; J.-R. Ohm; W.-J. Han; T.
Wiegand (December 2012). "Overview of the High Efficiency Video
Coding (HEVC) Standard" (PDF). IEEE Transactions on Circuits and
Systems for Video Technology (IEEE) 22 (12). Retrieved
2012-09-14.
Alternatively, video encoder 200 and video decoder 300 may operate
according to other proprietary or industry standards, such as ITU-T
H.266, also referred to as Versatile Video Coding (VVC). A draft of
the VVC standard is described in Bross, et al. "Versatile Video
Coding (Draft 5)," Joint Video Experts Team (JVET) of ITU-T SG 16
WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14.sup.th Meeting: Geneva, CH,
19-27 Mar. 2019, JVET-N1001-v9 (hereinafter "VVC Draft 5"). A more
recent draft of the VVC standard is described in Bross, et al.
"Versatile Video Coding (Draft 9)," Joint Video Experts Team (WET)
of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 18.sup.th
Meeting: by teleconference, 15-24 Apr. 2020, WET-R2001-v8
(hereinafter "VVC Draft 9"). The techniques of this disclosure,
however, are not limited to any particular coding standard.
In general, video encoder 200 and video decoder 300 may perform
block-based coding of pictures. The term "block" generally refers
to a structure including data to be processed (e.g., encoded,
decoded, or otherwise used in the encoding and/or decoding
process). For example, a block may include a two-dimensional matrix
of samples of luminance and/or chrominance data. In general, video
encoder 200 and video decoder 300 may code video data represented
in a YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red,
green, and blue (RGB) data for samples of a picture, video encoder
200 and video decoder 300 may code luminance and chrominance
components, where the chrominance components may include both red
hue and blue hue chrominance components. In some examples, video
encoder 200 converts received RGB formatted data to a YUV
representation prior to encoding, and video decoder 300 converts
the YUV representation to the RGB format. Alternatively, pre- and
post-processing units (not shown) may perform these
conversions.
This disclosure may generally refer to coding (e.g., encoding and
decoding) of pictures to include the process of encoding or
decoding data of the picture. Similarly, this disclosure may refer
to coding of blocks of a picture to include the process of encoding
or decoding data for the blocks, e.g., prediction and/or residual
coding. An encoded video bitstream generally includes a series of
values for syntax elements representative of coding decisions
(e.g., coding modes) and partitioning of pictures into blocks.
Thus, references to coding a picture or a block should generally be
understood as coding values for syntax elements forming the picture
or block.
HEVC defines various blocks, including coding units (CUs),
prediction units (PUs), and transform units (TUs). According to
HEVC, a video coder (such as video encoder 200) partitions a coding
tree unit (CTU) into CUs according to a quadtree structure. That
is, the video coder partitions CTUs and CUs into four equal,
non-overlapping squares, and each node of the quadtree has either
zero or four child nodes. Nodes without child nodes may be referred
to as "leaf nodes," and CUs of such leaf nodes may include one or
more PUs and/or one or more TUs. The video coder may further
partition PUs and TUs. For example, in HEVC, a residual quadtree
(RQT) represents partitioning of TUs. In HEVC, PUs represent
inter-prediction data, while TUs represent residual data. CUs that
are intra-predicted include intra-prediction information, such as
an intra-mode indication.
As another example, video encoder 200 and video decoder 300 may be
configured to operate according to VVC. According to VVC, a video
coder (such as video encoder 200) partitions a picture into a
plurality of coding tree units (CTUs). Video encoder 200 may
partition a CTU according to a tree structure, such as a
quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT)
structure. The QTBT structure removes the concepts of multiple
partition types, such as the separation between CUs, PUs, and TUs
of HEVC. A QTBT structure includes two levels: a first level
partitioned according to quadtree partitioning, and a second level
partitioned according to binary tree partitioning. A root node of
the QTBT structure corresponds to a CTU. Leaf nodes of the binary
trees correspond to coding units (CUs).
In an MTT partitioning structure, blocks may be partitioned using a
quadtree (QT) partition, a binary tree (BT) partition, and one or
more types of triple tree (TT) partitions. A triple tree partition
is a partition where a block is split into three sub-blocks. In
some examples, a triple tree partition divides a block into three
sub-blocks without dividing the original block through the center.
The partitioning types in MTT (e.g., QT, BT, and TT) may be
symmetrical or asymmetrical.
In some examples, video encoder 200 and video decoder 300 may use a
single QTBT or MTT structure to represent each of the luminance and
chrominance components, while in other examples, video encoder 200
and video decoder 300 may use two or more QTBT or MTT structures,
such as one QTBT/MTT structure for the luminance component and
another QTBT/MTT structure for both chrominance components (or two
QTBT/MTT structures for respective chrominance components).
Video encoder 200 and video decoder 300 may be configured to use
quadtree partitioning per HEVC, QTBT partitioning, MTT
partitioning, or other partitioning structures. For purposes of
explanation, the description of the techniques of this disclosure
is presented with respect to QTBT partitioning. However, it should
be understood that the techniques of this disclosure may also be
applied to video coders configured to use quadtree partitioning, or
other types of partitioning as well.
The blocks (e.g., CTUs or CUs) may be grouped in various ways in a
picture. As one example, a brick may refer to a rectangular region
of CTU rows within a particular tile in a picture. A tile may be a
rectangular region of CTUs within a particular tile column and a
particular tile row in a picture. A tile column refers to a
rectangular region of CTUs having a height equal to the height of
the picture and a width specified by syntax elements (e.g., such as
in a picture parameter set). A tile row refers to a rectangular
region of CTUs having a height specified by syntax elements (e.g.,
such as in a picture parameter set) and a width equal to the width
of the picture.
In some examples, a tile may be partitioned into multiple bricks,
each of which may include one or more CTU rows within the tile. A
tile that is not partitioned into multiple bricks may also be
referred to as a brick. However, a brick that is a true subset of a
tile may not be referred to as a tile.
The bricks in a picture may also be arranged in a slice. A slice
may be an integer number of bricks of a picture that may be
exclusively contained in a single network abstraction layer (NAL)
unit. In some examples, a slice includes either a number of
complete tiles or only a consecutive sequence of complete bricks of
one tile.
This disclosure may use "N.times.N" and "N by N" interchangeably to
refer to the sample dimensions of a block (such as a CU or other
video block) in terms of vertical and horizontal dimensions, e.g.,
16.times.16 samples or 16 by 16 samples. In general, a 16.times.16
CU will have 16 samples in a vertical direction (y=16) and 16
samples in a horizontal direction (x=16). Likewise, an N.times.N CU
generally has N samples in a vertical direction and N samples in a
horizontal direction, where N represents a nonnegative integer
value. The samples in a CU may be arranged in rows and columns.
Moreover, CUs need not necessarily have the same number of samples
in the horizontal direction as in the vertical direction. For
example, CUs may comprise N.times.M samples, where M is not
necessarily equal to N.
Video encoder 200 encodes video data for CUs representing
prediction and/or residual information, and other information. The
prediction information indicates how the CU is to be predicted in
order to form a prediction block for the CU. The residual
information generally represents sample-by-sample differences
between samples of the CU prior to encoding and the prediction
block.
To predict a CU, video encoder 200 may generally form a prediction
block for the CU through inter-prediction or intra-prediction.
Inter-prediction generally refers to predicting the CU from data of
a previously coded picture, whereas intra-prediction generally
refers to predicting the CU from previously coded data of the same
picture. To perform inter-prediction, video encoder 200 may
generate the prediction block using one or more motion vectors.
Video encoder 200 may generally perform a motion search to identify
a reference block that closely matches the CU, e.g., in terms of
differences between the CU and the reference block. Video encoder
200 may calculate a difference metric using a sum of absolute
difference (SAD), sum of squared differences (SSD), mean absolute
difference (MAD), mean squared differences (MSD), or other such
difference calculations to determine whether a reference block
closely matches the current CU. In some examples, video encoder 200
may predict the current CU using uni-directional prediction or
bi-directional prediction.
VVC may also provide an affine motion compensation mode, which may
be considered an inter-prediction mode. In affine motion
compensation mode, video encoder 200 may determine two or more
motion vectors that represent non-translational motion, such as
zoom in or out, rotation, perspective motion, or other irregular
motion types.
To perform intra-prediction, video encoder 200 may select an
intra-prediction mode to generate the prediction block. VVC may
provide sixty-seven intra-prediction modes, including various
directional modes, as well as planar mode and DC mode. In general,
video encoder 200 selects an intra-prediction mode that describes
neighboring samples to a current block (e.g., a block of a CU) from
which to predict samples of the current block. Such samples may
generally be above, above and to the left, or to the left of the
current block in the same picture as the current block, assuming
video encoder 200 codes CTUs and CUs in raster scan order (left to
right, top to bottom).
Video encoder 200 encodes data representing the prediction mode for
a current block. For example, for inter-prediction modes, video
encoder 200 may encode data representing which of the various
available inter-prediction modes is used, as well as motion
information for the corresponding mode. For uni-directional or
bi-directional inter-prediction, for example, video encoder 200 may
encode motion vectors using advanced motion vector prediction
(AMVP) or merge mode. Video encoder 200 may use similar modes to
encode motion vectors for affine motion compensation mode.
Following prediction, such as intra-prediction or inter-prediction
of a block, video encoder 200 may calculate residual data for the
block. The residual data, such as a residual block, represents
sample by sample differences between the block and a prediction
block for the block, formed using the corresponding prediction
mode. Video encoder 200 may apply one or more transforms to the
residual block, to produce transformed data in a transform domain
instead of the sample domain. For example, video encoder 200 may
apply a discrete cosine transform (DCT), an integer transform, a
wavelet transform, or a conceptually similar transform to residual
video data. Additionally, video encoder 200 may apply a secondary
transform following the first transform, such as a mode-dependent
non-separable secondary transform (MDNSST), a signal dependent
transform, a Karhunen-Loeve transform (KLT), or the like. Video
encoder 200 produces transform coefficients following application
of the one or more transforms.
As noted above, following any transforms to produce transform
coefficients, video encoder 200 may perform quantization of the
transform coefficients. Quantization generally refers to a process
in which transform coefficients are quantized to possibly reduce
the amount of data used to represent the coefficients, providing
further compression. By performing the quantization process, video
encoder 200 may reduce the bit depth associated with some or all of
the coefficients. For example, video encoder 200 may round an n-bit
value down to an m-bit value during quantization, where n is
greater than m. In some examples, to perform quantization, video
encoder 200 may perform a bitwise right-shift of the value to be
quantized.
This disclosure describes example ways in which video encoder 200
may determine the quantization parameter (QP) for a chroma block
for quantizing. The QP may be a value that defines an amount of
quantization that is to be applied the transform coefficients. In
some examples, video encoder 200 may determine the actual QP for a
chroma block (e.g., Cb or Cr chroma block) based on rate-distortion
measurements and signal information indicative of the actual
QP.
However, to reduce the number of bits that need to be signaled
(e.g., increase bandwidth), video encoder 200 may utilize a QP
predictor for the chroma block. In some examples, the QP predictor
may be the QP for the luma block corresponding to the chroma block
or based on QPs of a plurality of luma blocks. For instance, as
described above, a coding unit may include a luminance component
and/or a chrominance component. A luma block includes the samples
of the luminance component, and a chroma block includes the samples
of the chrominance component. Accordingly, for a coding unit there
may be one luma block and two chroma blocks (e.g., Cb chroma block
and Cr chroma block). A luma block and the two chroma blocks that
together form the coding unit may be referred to as corresponding
to one another because of the location of the chroma block and the
location of the luma block overlap.
Based on the color format, the size of the chroma blocks may be
different than the size of the luma blocks (e.g., the chroma blocks
are downsampled relative to the luma blocks). For instance, in
4:2:0 color format, the luma block is N.times.N and in size the
chroma block is N/2.times.N/2 in size. In this example, one chroma
block of size N.times.N would correspond with four N.times.N sized
luma blocks.
In some examples, the QP for the luma block (e.g., luma QP) may be
a QP predictor for the QPs for both of the corresponding chroma
blocks. In some examples, a plurality of luma blocks may be
correspond to one chroma block, and some average of the luma QPs of
the plurality of luma blocks may be a QP predictor for the QPs for
both of the corresponding chroma blocks. In any event, video
encoder 200 may determine a quantization parameter predictor for a
chroma block of video data based on a quantization parameter for a
corresponding luma block.
Video encoder 200 may also determine an offset value, such that
when the offset value is added to the QP predictor, the result is
the quantization parameter for the chroma block. In accordance with
one or more examples described in this disclosure, video encoder
200 may determine block level quantization parameter offset for a
chroma block that when added to the QP predictor (possibly with
some additional offsets), the result is the quantization parameter
for a chroma block.
Block level quantization parameter offset may refer to quantization
parameter offset that can be different on block-by-block basis. For
instance, in some techniques, video encoder 200 may be limited to
signaling high-level offsets, such as picture level offsets or
slice level offsets, that are the same for all chroma blocks in a
picture or slice. In some of those techniques, there may be no way
in which to define, at a block level, what the offset should be.
That is, there may not be block level granularity to define the
offset for a chroma block. Rather, the offset would be the same for
all blocks in the picture or slice.
In some of those techniques, where the offset is the same for all
blocks in the picture or slice, utilizing the same offset to
determine the quantization parameters for each of the chroma blocks
may result in some of the chroma blocks having suboptimal
quantization parameters. For instance, if the slice level or
picture level offset is equal to A and B, respectively, Y1 is the
quantization parameter predictor for a first chroma block in the
slice, and Y2 is the quantization parameter predictor for a second
chroma block in the slice, then the quantization parameter for the
first chroma block would be Y1+A+B and the quantization parameter
for the second chroma block would be Y2+A+B. In some of those
techniques, there may not be a way in which to define a block level
quantization parameter offset for the first chroma block that is
different than the block level quantization parameter offset for
the second chroma block. Rather, the quantization parameter offset
is limited to A and B for both the first and the second chroma
blocks.
In accordance with techniques described in this disclosure, video
encoder 200 may determine a block level quantization parameter
offset for a chroma block, and determine a quantization parameter
for the chroma block based on the block level quantization
parameter offset and the quantization parameter predictor. For
instance, there may be N number of possible block level
quantization parameter offsets to select from, and video encoder
200 may select a block level quantization parameter offset that
when added to the quantization parameter predictor (possibly with
other offsets as well) results in the best quantization parameter
for the chroma block. Video encoder 200 may then quantize
coefficient values for a residual block based on the determined
quantization parameter for the chroma block, and signal information
indicative of the quantized coefficient values.
As described above, there may be two chroma blocks (e.g., Cb and Cr
chroma blocks). In one or more examples, video encoder 200 may
perform similar operations for both Cb chroma block and Cr chroma
block. In some examples, there may be a joint chroma block that is
a combination of the Cb and Cr chroma blocks (e.g., JointCbCr
chroma block), and the example techniques described in this
disclosure are applicable to the JointCbCr chroma block as well.
Accordingly, in the above examples that refer to a chroma block,
the chroma block may be a Cb chroma block, a Cr chroma block, or a
JointCbCr chroma block.
Following quantization, video encoder 200 may scan the transform
coefficients, producing a one-dimensional vector from the
two-dimensional matrix including the quantized transform
coefficients. The scan may be designed to place higher energy (and
therefore lower frequency) coefficients at the front of the vector
and to place lower energy (and therefore higher frequency)
transform coefficients at the back of the vector. In some examples,
video encoder 200 may utilize a predefined scan order to scan the
quantized transform coefficients to produce a serialized vector,
and then entropy encode the quantized transform coefficients of the
vector. In other examples, video encoder 200 may perform an
adaptive scan. After scanning the quantized transform coefficients
to form the one-dimensional vector, video encoder 200 may entropy
encode the one-dimensional vector, e.g., according to
context-adaptive binary arithmetic coding (CABAC). Video encoder
200 may also entropy encode values for syntax elements describing
metadata associated with the encoded video data for use by video
decoder 300 in decoding the video data.
To perform CABAC, video encoder 200 may assign a context within a
context model to a symbol to be transmitted. The context may relate
to, for example, whether neighboring values of the symbol are
zero-valued or not. The probability determination may be based on a
context assigned to the symbol.
Video encoder 200 may further generate syntax data, such as
block-based syntax data, picture-based syntax data, and
sequence-based syntax data, to video decoder 300, e.g., in a
picture header, a block header, a slice header, or other syntax
data, such as a sequence parameter set (SPS), picture parameter set
(PPS), or video parameter set (VPS). Video decoder 300 may likewise
decode such syntax data to determine how to decode corresponding
video data.
In this manner, video encoder 200 may generate a bitstream
including encoded video data, e.g., syntax elements describing
partitioning of a picture into blocks (e.g., CUs) and prediction
and/or residual information for the blocks. Ultimately, video
decoder 300 may receive the bitstream and decode the encoded video
data.
In general, video decoder 300 performs a reciprocal process to that
performed by video encoder 200 to decode the encoded video data of
the bitstream. For example, video decoder 300 may decode values for
syntax elements of the bitstream using CABAC in a manner
substantially similar to, albeit reciprocal to, the CABAC encoding
process of video encoder 200. The syntax elements may define
partitioning information of a picture into CTUs, and partitioning
of each CTU according to a corresponding partition structure, such
as a QTBT structure, to define CUs of the CTU. The syntax elements
may further define prediction and residual information for blocks
(e.g., CUs) of video data.
The residual information may be represented by, for example,
quantized transform coefficients. Video decoder 300 may inverse
quantize and inverse transform the quantized transform coefficients
of a block to reproduce a residual block for the block. For
example, video decoder 300 may be configured to determine a
quantization parameter for a chroma block using the example
techniques described in this disclosure.
As described above, video encoder 200 may be configured to
determine a quantization parameter predictor for a chroma block.
Video decoder 300 may perform similar operations to determine a
quantization parameter predictor for a chroma block of video data
based on a quantization parameter for a corresponding luma block.
The quantization parameter predictor may be the quantization
parameter of the corresponding luma block or may be some average of
the quantization parameters of a plurality of luma blocks that may
correspond to the chroma block. In general, the quantization
parameter predictor may be determined based on the quantization
parameter of the corresponding luma block, and need not necessarily
be the quantization parameter of the corresponding luma block.
Video decoder 300 may also determine a block level quantization
parameter offset for the chroma block. For instance, video encoder
200 may signal information to video decoder 300 that video decoder
300 uses to determine the block level quantization parameter
offset. As one example, as described above, there may be N number
of possible block level quantization parameter offsets for video
encoder 200 to select from, and video encoder 200 may signal
information indicating which one of the N number of possible block
level quantization parameter offsets video decoder 300 is to
select.
To determine the quantization parameter for the chroma block, video
decoder 300 may determine a quantization parameter for the chroma
block based on the block level quantization parameter offset and
the quantization parameter predictor. For instance, video decoder
300 may add the block level quantization parameter offset to the
quantization parameter predictor (and possibly add some additional
other offsets) to determine the quantization parameter for the
chroma block.
Video decoder 300 may determine a residual block based on the
quantization parameter. For instance, video decoder 300 may perform
the inverse quantization based on the quantization parameter to
determine the residual block.
Video decoder 300 may use a signaled prediction mode (intra- or
inter-prediction) and related prediction information (e.g., motion
information for inter-prediction) to form a prediction block for
the block. Video decoder 300 may then combine the prediction block
and the residual block (on a sample-by-sample basis) to reproduce
the original block. For example, video decoder 300 may reconstruct
the chroma block based on the residual block. Video decoder 300 may
perform additional processing, such as performing a deblocking
process to reduce visual artifacts along boundaries of the
block.
This disclosure may generally refer to "signaling" certain
information, such as syntax elements. The term "signaling" may
generally refer to the communication of values for syntax elements
and/or other data used to decode encoded video data. That is, video
encoder 200 may signal values for syntax elements in the bitstream.
In general, signaling refers to generating a value in the
bitstream. As noted above, source device 102 may transport the
bitstream to destination device 116 substantially in real time, or
not in real time, such as might occur when storing syntax elements
to storage device 112 for later retrieval by destination device
116.
As described above, in one or more examples, video encoder 200 and
video decoder 300 may be configured to determine quantization
parameters for chroma blocks using block level quantization
parameter offsets. For instance, video encoder 200 and video
decoder 300 may utilize similar techniques to determine a
quantization parameter predictor for a chroma block of the video
data based on a quantization parameter for a corresponding luma
block. The quantization parameter predictor may be the quantization
parameter of the corresponding luma block or may be an average of
quantization parameters of a plurality of corresponding luma
blocks, or some other technique that utilizes the quantization
parameter of the corresponding luma block may be used to determine
the quantization parameter predictor.
Video encoder 200 and video decoder 300 may determine a block level
quantization parameter offset for the chroma block. The block level
quantization parameter offset for the chroma block may mean that
the block level quantization parameter offset can be different for
different chroma blocks in same slice or picture. For instance, a
slice may include two or more chroma blocks. In one or more
examples, a first block level quantization parameter offset for a
first chroma block in the slice and a second block level
quantization parameter offset for a second chroma block in the same
slice may be different.
In one or more examples, video encoder 200 and video decoder 300
may determine a quantization parameter for the chroma block based
on the block level quantization parameter offset and the
quantization parameter predictor. In addition to the block level
quantization parameter offset, there may be a first quantization
parameter offset in a picture parameter set and a second
quantization parameter offset in a slice parameter set (e.g., slice
header). For instance, video encoder 200 may signal and video
decoder 300 may receive the first quantization parameter offset
from a picture parameter set (PPS), and video encoder 200 may
signal and video decoder 300 may receive the second quantization
parameter from a slice parameter set (e.g., information signaled at
the slice level). Video encoder 200 and video decoder 300 may add
the first quantization parameter offset, the second quantization
parameter offset, the block level quantization parameter offset,
and the quantization parameter predictor to determine the
quantization parameter for the chroma block.
Based on the quantization parameter, video encoder 200 and video
decoder 300 may perform quantizing or inverse-quantizing. For
example, video encoder 200 may quantize coefficient values for a
residual block based on the determined quantization parameter for
the chroma block. Video decoder 300 may inverse-quantize received
values to generate the residual block based on the determined
quantization parameter for the chroma block. Video encoder 200 may
signal information indicative of the quantized coefficient values.
Video decoder 300 may add the residual block to a prediction block
to reconstruct the chroma block.
As described, video encoder 200 and video decoder 300 may be
configured to determine the block level quantization parameter
offset for the chroma block. In some examples, there may be N block
level quantization parameter offsets from which to select the block
level quantization parameter offset for the chroma block. For
instance, video encoder 200 may construct a list of quantization
parameter offsets, which include the N block level quantization
parameter offsets from which to select the block level quantization
parameter offset for a chroma block. Video encoder 200 may signal
information indicating the values in the list of quantization
parameter offsets to video decoder 300, and video decoder 300 may
construct the list of quantization parameter offsets based on the
signaled information.
However, in some examples, the list of quantization parameter
offsets may be predefined and pre-stored. In some examples, video
encoder 200 and video decoder 300 may each follow similar
operations to construct the list of quantization parameter offsets
using implicit techniques that do not require video encoder 200 to
signal to video decoder 300 the information for constructing the
list of quantization parameter offsets. There may be various ways
in which to construct the list of quantization parameter offsets
(e.g., signaling, pre-stored, or implicit), and the example
techniques are not limited to any particular way in which video
encoder 200 and video decoder 300 construct the list of
quantization parameter offsets.
In one or more examples, video encoder 200 may determine which
quantization parameter offset to select from the list of
quantization parameter offsets and signal an index into the list of
quantization parameter offsets. Video decoder 300 may receive an
index into the list of quantization parameter offsets and determine
the block level quantization parameter offset based on the index
into the list of quantization parameter offsets.
Video encoder 200 and video decoder 300 may perform similar
operations to determine block level quantization parameter offsets
for each of the chroma blocks for the different chroma components.
For instance, video encoder 200 and video decoder 300 may construct
a first list of quantization parameter offsets for the Cb chroma
block and a second list of quantization parameter offsets for the
Cr chroma block.
For instance, there may be a luma block and two chroma blocks
(e.g., one chroma block for each chroma component). There may be a
Cb chroma block (e.g., a first chroma block of a first chroma
component) and a Cr chroma block (e.g., a second chroma block of a
second chroma component). In this example, the Cb chroma block and
the Cr chroma block may share the same quantization parameter
predictor (e.g., because the Cb chroma block and Cr chroma block
correspond to the same luma block or plurality of luma blocks).
However, the block level quantization parameter offset for the Cb
chroma block and the Cr chroma block may be different. It is
possible for the quantization parameter predictor for the Cb chroma
block and the Cr chroma block to be different.
Although the block level quantization parameter offset for the Cb
chroma block and Cr chroma block may be different, video encoder
200 and video decoder 300 may utilize the same index into
respective lists of quantization parameter offsets. For example,
video encoder 200 may signal and video decoder 300 may receive an
index into the first list of quantization parameter offsets for the
first chroma block of the first color component (e.g., Cb chroma
block) to determine the quantization parameter for the first chroma
block of the first color component. Video encoder 200 and video
decoder 300 may utilize the same index into the second list of
quantization parameter offsets for the second chroma block of the
second color component (e.g., Cr chroma block) to determine the
quantization parameter for the second chroma block of the second
color component. Accordingly, there may be two lists of
quantization parameter offsets, but only one index may be
needed.
FIGS. 2A and 2B are conceptual diagram illustrating an example
quadtree binary tree (QTBT) structure 130, and a corresponding
coding tree unit (CTU) 132. The solid lines represent quadtree
splitting, and the dotted lines indicate binary tree splitting. In
each split (i.e., non-leaf) node of the binary tree, one flag is
signaled to indicate which splitting type (i.e., horizontal or
vertical) is used, where 0 indicates horizontal splitting and 1
indicates vertical splitting in this example. For the quadtree
splitting, there is no need to indicate the splitting type, since
quadtree nodes split a block horizontally and vertically into 4
sub-blocks with equal size. Accordingly, video encoder 200 may
encode, and video decoder 300 may decode, syntax elements (such as
splitting information) for a region tree level of QTBT structure
130 (i.e., the solid lines) and syntax elements (such as splitting
information) for a prediction tree level of QTBT structure 130
(i.e., the dotted lines). Video encoder 200 may encode, and video
decoder 300 may decode, video data, such as prediction and
transform data, for CUs represented by terminal leaf nodes of QTBT
structure 130.
In general, CTU 132 of FIG. 2B may be associated with parameters
defining sizes of blocks corresponding to nodes of QTBT structure
130 at the first and second levels. These parameters may include a
CTU size (representing a size of CTU 132 in samples), a minimum
quadtree size (MinQTSize, representing a minimum allowed quadtree
leaf node size), a maximum binary tree size (MaxBTSize,
representing a maximum allowed binary tree root node size), a
maximum binary tree depth (MaxBTDepth, representing a maximum
allowed binary tree depth), and a minimum binary tree size
(MinBTSize, representing the minimum allowed binary tree leaf node
size).
The root node of a QTBT structure corresponding to a CTU may have
four child nodes at the first level of the QTBT structure, each of
which may be partitioned according to quadtree partitioning. That
is, nodes of the first level are either leaf nodes (having no child
nodes) or have four child nodes. The example of QTBT structure 130
represents such nodes as including the parent node and child nodes
having solid lines for branches. If nodes of the first level are
not larger than the maximum allowed binary tree root node size
(MaxBTSize), then the nodes can be further partitioned by
respective binary trees. The binary tree splitting of one node can
be iterated until the nodes resulting from the split reach the
minimum allowed binary tree leaf node size (MinBTSize) or the
maximum allowed binary tree depth (MaxBTDepth). The example of QTBT
structure 130 represents such nodes as having dotted lines for
branches. The binary tree leaf node is referred to as a coding unit
(CU), which is used for prediction (e.g., intra-picture or
inter-picture prediction) and transform, without any further
partitioning. As discussed above, CUs may also be referred to as
"video blocks" or "blocks."
In one example of the QTBT partitioning structure, the CTU size is
set as 128.times.128 (luma samples and two corresponding
64.times.64 chroma samples), the MinQTSize is set as 16.times.16,
the MaxBTSize is set as 64.times.64, the MinBTSize (for both width
and height) is set as 4, and the MaxBTDepth is set as 4. The
quadtree partitioning is applied to the CTU first to generate
quad-tree leaf nodes. The quadtree leaf nodes may have a size from
16.times.16 (i.e., the MinQTSize) to 128.times.128 (i.e., the CTU
size). If the leaf quadtree node is 128.times.128, it will not be
further split by the binary tree, since the size exceeds the
MaxBTSize (i.e., 64.times.64, in this example). Otherwise, the leaf
quadtree node will be further partitioned by the binary tree.
Therefore, the quadtree leaf node is also the root node for the
binary tree and has the binary tree depth as 0. When the binary
tree depth reaches MaxBTDepth (4, in this example), no further
splitting is permitted. When the binary tree node has width equal
to MinBTSize (4, in this example), it implies no further horizontal
splitting is permitted. Similarly, a binary tree node having a
height equal to MinBTSize implies no further vertical splitting is
permitted for that binary tree node. As noted above, leaf nodes of
the binary tree are referred to as CUs, and are further processed
according to prediction and transform without further
partitioning.
The following describes some video coding standards. Video coding
standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262
or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and
ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its
Scalable Video Coding (SVC) and Multi-view Video Coding (MVC)
extensions.
In addition, High Efficiency Video Coding (HEVC) or ITU-T H.265,
including its range extension, multiview extension (MV-HEVC) and
scalable extension (SHVC), has been developed by the Joint
Collaboration Team on Video Coding (JCT-VC) as well as Joint
Collaboration Team on 3D Video Coding Extension Development
(JCT-3V) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC
Motion Picture Experts Group (MPEG). The latest HEVC draft
specification, and referred to as HEVC WD hereinafter, is available
from
http://phenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/-
JCTVC-N1003-v1.zip.
There may be certain issues in current techniques for determining
chroma quantization parameter (QP). As described above, the QP
indicates the amount by which to quantize or inverse-quantize
coefficients in a block.
In VVC Draft 5, a chroma QP is derived as below:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset-
+slice_cr_qp_offset)
In the above equation, qPi.sub.Cb is the quantization parameter for
the Cb chroma block, and qPi.sub.Cr is the quantization parameter
for the Cr chroma block. Qp.sub.Y is a quantization parameter
predictor, and in some examples is the quantization parameter for a
corresponding luma block to the Cb chroma block and the Cr chroma
block. Qp.sub.Y being the quantization parameter predictor is
merely one example. The quantization parameter predictor may be
based on Qp.sub.Y without necessarily being equal to Qp.sub.Y
(e.g., the quantization parameter predictor may be determined as a
function of Qp.sub.Y).
The syntax element pps_cb_qp_offset is an offset value signaled in
the picture parameter set for the Cb chroma block, and the syntax
element pps_cr_qp_offset is an offset value signaled in the picture
parameter set for the Cr chroma block. The syntax element
slice_cb_qp_offset is an offset value signaled in the slice
parameter set (e.g., such as slice header) for the Cb chroma block,
and the syntax element slice_cr_qp_offset is an offset value
signaled in the slice parameter set for the Cr chroma block. The
value of QpBdOffset.sub.C may be a preselected or determined
value.
Accordingly, in VVC Draft 5, the value of qPi.sub.Cb is equal to
Qp.sub.Y+pps_cb_qp_offset+slice_cb_qp_offset, but clipped to within
-QpBdOffset.sub.C and 69 if
Qp.sub.Y+pps_cb_qp_offset+slice_cb_qp_offset is outside that range.
Similarly, in VVC Draft 5, the value of qPi.sub.Cr is equal to
Qp.sub.Y+pps_cr_qp_offset+slice_cr_qp_offset, but clipped to within
-QpBdOffset.sub.C and 69 if
Qp.sub.Y+pps_cr_qp_offset+slice_cr_qp_offset is outside that
range.
As described above and also described in more detail below,
pps_cb_qp_offset and slice_cb_qp_offset apply to all Cb chroma
blocks in a picture or slice. Therefore, there may not be block
level quantization parameter offsets that can be used to determine
the qPi.sub.Cr value for a Cb chroma block. Similarly,
pps_cr_qp_offset and slice_cr_qp_offset apply to all Cr chroma
blocks in a picture or slice. Therefore, there may not be block
level quantization parameter offsets that can be used to determine
the qPi.sub.Cr value for a Cr chroma block. This disclosure
describes example techniques for utilizing block level quantization
parameter offset for determining the quantization parameter for the
Cb chroma block (e.g., qPi.sub.Cb) and the quantization parameter
for the Cr chroma block (e.g., qPi.sub.Cr)
For instance, when the tree type is a separate tree type (e.g.,
chroma and luma blocks are partitioned independently), the variable
Qp.sub.Y is set equal to the luma QP of the luma CB (coding block)
that covers the luma position (xCb+cbWidth/2, yCb+cbHeight/2). As
shown in FIG. 5, one chroma coding block (CB) 402 may cover more
than one luma CBs. For example, chroma CB 402 covers luma CBs
400A-400D. These luma CBs 400A-400D can be from different
quantization groups (QGs) with different QPs. The predicted QP
derived from the center position may be not an accurate prediction
for the chroma CB, and picture parameter set (PPS)/slice level QP
offset adjustment is limited (e.g., pps_cr_qp_offset and
slice_cr_qp_offset and pps_cb_qp_offset and slice_cb_qp_offset may
be limited). There may be no scheme of flexible adjusting chroma QP
in the current VVC.
One example way in which to address some deficiencies with flexible
adjustment of chroma QP is to fix the luma delta QP signaling in
VVC. For instance, in VVC Draft 5, the condition of signaling luma
delta QP may not be correct. Partial syntax is as below.
TABLE-US-00001 if( ( tu_cbf_luma[ x0 ][ y0 ] | | tu_cbf_cb[ x0 ][
y0 ] | | tu_cbf_cr[ x0 ][ y0 ]) && treeType !=
DUAL_TREE_CHROMA) { if( cu_qp_delta_enabled_flag &&
!IsCuQpDeltaCoded ) { cu_qp_delta_abs ae(v) if( cu_qp_delta_abs)
cu_qp_delta_sign_flag ae(v) } }
According to the syntax, when treeType equals to DUAL_TREE_LUMA,
and tu_cbf_luma equals to 0, and tu_cbf_cb or tu_cbf_cr equals to
1, luma delta QP still can be signaled. Signaling of luma delta QP
in this case may be erroneous (e.g., unnecessary or cause video
decoder 300 to perform in an unexpected manner). When the tree type
is dual tree luma, the luma delta QP signaling may not (e.g.,
should not) depend on the CBF flag (coded bit flag indicating
whether any bit in the block is significant) of chroma (tu_cbf_cb,
tu_cbf_cr). For example, CBF flags of tu_cbf_luma[x0][y0],
tu_cbf_cb[x0][y0],
tu_cbf_cr[x0][y0] equals to 1 means there is coding bin in the
coding block. Otherwise, CBF equals to 0 means there is no coding
bin in the coding block. In one example, the disclosure describes
modifications to the condition of luma delta QP signaling. When the
tree type is dual tree luma, the luma delta QP signaling may depend
on luma CBF flag, and may not (e.g., does not) depend on chroma CBF
flag. The partial syntax is as below: where new syntax is shown
with text between <ADD> and </ADD> and removed syntax
is shown with text between <DELETE> and </DELETE>
TABLE-US-00002 <ADD> If(treeType != DUAL_TREE_CHROMA) {
</ADD> if((( tu_cbf_luma[ x0 ][ y0 ] | | tu_cbf_cb[ x0 ][ y0
] | | tu_cbf_cr[ x0 ][ y0 ] ) <DELETE> && treeType !=
DUAL_TREE_CHROMA </DELETE> <ADD> && treeType !=
DUAL_TREE_LUMA ) || (tu_cbf_luma[ x0 ] [ y0 ] && treeType
== DUAL_TREE_LUMA </ADD>) ) { if( cu_qp_delta_enabled_flag
&& !IsCuQpDeltaCoded ) { cu_qp_delta_abs ae(v) if(
cu_qp_delta_abs ) cu_qp_delta_sign_flag ae(v) } } <ADD> }
</ADD>
In one example, video encoder 200 and video decoder 300 may be
configured to apply the CU level chroma QP offset method of HEVC
range extension directly to VVC (e.g., extended CU chroma QP offset
from Cb, Cr components to joint_cbcr (joint coding of chrominance
residuals, JCCR)).
The partial syntax is as below. Underline shows addition.
TABLE-US-00003 <ADD> If(( tu_cbf_cb[ x0 ] [ y0 ] | |
tu_cbf_cr[ x0 ] [ y0 ] ) &&
cu_chroma_qp_offset_enabled_flag &&
!IsCuChromaQpOffsetCoded ) { cu_chroma_qp_offset_flag ae(v) if(
cu_chroma_qp_offset_flag &&
chroma_qp_offset_list_len_minus1 > 0 ) cu_chroma_qp_offset_idx
ae(v) } </ADD>
In the above syntax elements, the syntax elements tu_cbf_cb and
tu_cbf_cr indicate whether there are any residual values for a Cb
chroma block or the Cr chroma block. If there are no residual
values, then no quantization or inverse quantization is needed.
However, if there are residual values for the Cb chroma block or
the Cr chroma block, then video encoder 200 may determine
quantization parameters for quantizing and video decoder 300 may
determine quantization parameters for inverse quantizing.
As described above and in more detail below, this disclosure
describes examples of block level quantization parameter offsets
for determining the quantization parameter for a chroma block.
Because the example quantization parameter offsets are at the block
level, the block level quantization parameter offsets may be
considered as being at the CU level.
In the above syntax elements, cu_chroma_qp_offset_enabled_flag
indicates whether block level quantization parameter offsets are
enabled or not (e.g., for blocks in a slice or a picture). The
cu_chroma_qp_offset_flag indicates whether block level quantization
parameter offsets are enabled or not for a particular chroma block.
For example, if cu_chroma_qp_offset_enabled_flag is true, it means
that it is possible for the quantization parameter of a chroma
block to be determined based on a block level quantization
parameter offset. However, it does not necessarily mean that the
quantization parameter of a particular chroma block is to be
determined based on a block level quantization parameter offset.
The cu_chroma_qp_offset_flag may indicate whether the quantization
parameter of a particular chroma block is to be determined based on
a block level quantization parameter offset.
If the quantization parameter of a particular chroma block is to be
determined based on a block level quantization parameter offset
(e.g., cu_chroma_qp_offset_flag is true), then video encoder 200
may signal and video decoder 300 may receive the
cu_chroma_qp_offset_idx, which is an index into a list of
quantization parameter offsets, referred to as cb_qp_offset_list
for the Cb chroma block and cr_qp_offset_list for the Cr chroma
block. The cu_chroma_qp_offset_idx may identify a block level
quantization parameter offset, and video encoder 200 and video
decoder 300 may utilize the block level quantization parameter
offset to determine the quantization parameter for the chroma
block. In one or more examples, the same cu_chroma_qp_offset_idx
may be used to identify the block level quantization parameter
offset for the Cb chroma block from cb_qp_offset_list and to
identify the block level quantization parameter offset for the Cr
chroma block from cr_qp_offset_list.
In other words, a chroma QP offset index (e.g.,
cu_chroma_qp_offset_idx) is signaled at CU level (e.g., block
level). Video decoder 300 may use this index to determine the block
level quantization parameter offset. The Cb block level
quantization parameter offset for a Cb chroma block may be referred
to as CuQpOffsetCb. The Cr block level quantization parameter
offset for a Cr chroma block may be referred to as CuQpOffsetCr.
The JointCbCr block level quantization parameter offset for a
JointCbCr chroma block may be referred to as CuQpOffsetJointCbCr.
CuQpOffsetCb, CuQpOffsetCr, and CuQpOffsetJointCbCr are identified
from the list of quantization parameter offsets, which may be a
lookup table.
In some examples, even if block level quantization parameter offset
is to be used for a particular block, video encoder 200 may not
signal and video decoder 300 may not receive an index into the list
of quantization parameter offsets. For example, if the size of list
of quantization parameter offsets is only one, then video encoder
200 and video decoder 300 may implicitly determine that the index
into the list of quantization parameter offsets is the first entry
in the list of quantization parameter offsets without needing to
signal any index.
In one example, the chroma QP offset lookup table (e.g., the list
of quantization parameter offsets) can be predefined in both video
encoder 200 and video decoder 300 or signaled from video encoder
200 to video decoder 300 at sequence level, picture level, or slice
level. For example, this value can be signaled in a Sequence
Parameter Set (SPS), a Picture Parameter Set (PPS), and/or a Slice
header (SH). That is, the values that make the list of quantization
parameter offset (e.g., cb_qp_offset_list, cr_qp_offset_list, or
joint_cbcr_qp_offset_list) may be pre-stored in video encoder 200
and video decoder 300 or video encoder 200 may signal and video
decoder 300 may receive the values in an SPS, PPS, and/or SH.
The following describes example ways in which the block level
quantization parameter offset is utilized to determine the
quantization parameter for a chroma block. The block level
quantization parameter offset may be CuQpOffsetCb, CuQpOffsetCr,
and CuQpOffsetJointCbCr that are identified from respective lists
of quantization parameter offsets (e.g., cb_qp_offset_list,
cr_qp_offset_list, or joint_cbcr_qp_offset_list) based on a
signaled index (e.g., cu_chroma_qp_offset_idx).
In one example, the variables qPi.sub.Cb, qPi.sub.Cr and
qPi.sub.CbCr can be derived as follows:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . +CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . +CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_c bcr_qp_offset+ . . . +CuQpOffsetJointCbCr)
In the above,
CuQpOffsetCb=cb_qp_offset_list[cu_chroma_qp_offset_idx] is the CU
level QP offset for Cb and
CuQpOffsetCr=cr_qp_offset_list[cu_chroma_qp_offset_idx] is the CU
level QP offset for Cr, and
CuQpOffsetJointCbCr=joint_cbcr_qp_offset_list[cu_chroma_qp_offset_idx]
is the CU level QP offset for joint CbCr. For example, to determine
CuQpOffsetCb (e.g., block level quantization parameter offset for
Cb chroma block), video encoder 200 and video decoder 300 may
construct a list of quantization parameter offsets (e.g.,
cb_qp_offset_list). Video encoder 200 may signal an index (e.g.,
cu_chroma_qp_offset_idx) into the list of quantization parameter
offsets. Video decoder 300 may determine that the value stored in
cb_qp_offset_list[cu_chroma_qp_offset_idx] is equal to
CuQpOffsetCb. To determine CuQpOffsetCr (e.g., block level
quantization parameter offset for Cr chroma block), video encoder
200 and video decoder 300 may construct a list of quantization
parameter offsets (e.g., cr_qp_offset_list). Video encoder 200 may
signal an index (e.g., cu_chroma_qp_offset_idx) into the list of
quantization parameter offsets. Video decoder 300 may determine
that the value stored in cr_qp_offset_list[cu_chroma_qp_offset_idx]
is equal to CuQpOffsetCr. In this example, the same index (e.g.,
cu_chroma_qp_offset_idx) is used to identify the block level
quantization parameter offset for the Cb chroma block and the Cr
chroma block. To determine CuQpOffsetJointCbCr (e.g., block level
quantization parameter offset for JointCbCr chroma block), video
encoder 200 and video decoder 300 may construct a list of
quantization parameter offsets (e.g., jointcbcr_qp_offset_list).
Video encoder 200 may signal an index (e.g.,
cu_chroma_qp_offset_idx) into the list of quantization parameter
offsets. Video decoder 300 may determine that the value stored in
jointcbcr_qp_offset_list[cu_chroma_qp_offset_idx] is equal to
CuQpOffsetJointCbCr.
As described above, the equations to determine the quantization
parameter for the Cb chroma block, Cr chroma block, and JointCbCr
chroma block may be as follows:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . +CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . +CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_cbcr qp_offset+ . . . +CuQpOffsetJointCbCr)
Accordingly, in accordance with one or more examples described in
this disclosure, video decoder 300 may be configured to determine a
quantization parameter predictor for a chroma block of video data
based on a quantization parameter for a corresponding luma block.
As one example, the quantization parameter predictor is Qp.sub.Y,
and may be the quantization parameter for a corresponding luma
block or average of plurality of corresponding luma blocks. In some
examples, the quantization parameter predictor may be determined
based on Qp.sub.Y without necessarily being equal to Qp.sub.Y. For
example, the Qp.sub.Y may form as a value into a look up table from
which the quantization parameter predictor is determined. The
quantization parameter predictor may be different for the different
chroma components or may be the same for the different chroma
components.
Video decoder 300 may determine a block level quantization
parameter offset for the chroma block. Examples of the block level
quantization parameter offset include CuQpOffsetCb for the Cb
chroma block, CuQpOffsetCr for the Cr chroma block, and
CuQpOffsetJointCbCr for the JointCbCr chroma block.
In one or more examples, the block level quantization parameter
offset is different for at least one other chroma block in same
slice or picture as the chroma block and is determined on a chroma
block-by-chroma block basis. For instance, a first chroma block in
a slice or picture may have a different block level quantization
parameter offset as a second chroma block in the same slice or
picture, and the block level quantization parameter offset for the
first block and the second block may be determined on a chroma
block-by-chroma block basis.
As one example, the first chroma block may be of a first chroma
component (e.g., Cb chroma block or Cr chroma block) and the second
chroma block may be of a second chroma component (e.g., the other
of Cb chroma block or Cr chroma block). In this example, video
decoder 300 may determine a first block level quantization
parameter offset for the first chroma block of the first chroma
component and determine a second block level quantization parameter
offset for the second chroma block of the second chroma component.
The first block level quantization parameter offset and the second
block level quantization parameter offset may be different.
In the above example, the first chroma block and the second chroma
block are of the same CU. However, in some examples, the first
chroma block and the second chroma block may be of different CUs,
and the block level quantization parameter offset for the first
chroma block and the second chroma block of different CUs may be
different.
There may be various ways in which video decoder 300 may determine
the block level quantization parameter offset. For example, video
decoder 300 may construct a list of quantization parameter offsets
(e.g., cb_qp_offset_list, cr_qp_offset_list, and/or
joint_cbcr_qp_offset_list), where the values for the list of
quantization parameter offsets may be pre-stored or signaled. Video
decoder 300 may receive an index into the list of quantization
parameter offsets (e.g., cu_chroma_qp_offset_idx). Video decoder
300 may determine the block level quantization parameter offset
based on the index into the list of quantization parameter offsets.
For example, video decoder 300 may determine that
cb_qp_offset_list[cu_chroma_qp_offset_idx] is the CU level QP
offset for Cb and
CuQpOffsetCr=cr_qp_offset_list[cu_chroma_qp_offset_idx] is the CU
level QP offset for Cr, and
CuQpOffsetJointCbCr=joint_cbcr_qp_offset_list[cu_chroma_qp_offset_idx]
is the CU level QP offset for JointCbCr.
In one or more examples, where a first chroma block and a second
chroma block are of the same CU, the index into respective lists of
quantization parameter offsets may be the same. For example,
cu_chroma_qp_offset_idx is the index for both cb_qp_offset_list and
cr_qp_offset_list. That is, video decoder 300 may be configured to
determine a first block level quantization parameter offset from an
index into a first list of quantization parameter offsets for the
first chroma component (e.g., determine CuQpOffsetCb based on
cu_chroma_qp_offset_idx into cb_qp_offset_list), and determine the
second block level quantization parameter offset from the same
index into a second list of quantization parameter offsets for the
second chroma component (e.g., determine CuQpOffsetCr based on
cu_chroma_qp_offset_idx into cr_qp_offset_list).
Video decoder 300 may determine a quantization parameter for the
chroma block based on the block level quantization parameter offset
and the quantization parameter predictor. For example, video
decoder 300 may receive at least one of a first quantization
parameter offset for chroma component in a picture parameter set
(e.g., pps_cb_qp_offset for Cb chroma block or pps_cr_qp_offset for
Cr chroma block) or a second quantization parameter offset for
chroma component in a slice parameter set (e.g., slice_cb_qp_offset
for Cb chroma block or slice_cr_qp_offset for Cr chroma block
signaled in slice header).
Video decoder 300 may determine the quantization parameter for the
chroma block by adding the block level quantization parameter
offset and one or both of the first quantization parameter offset
and the second quantization parameter offset. For example, as
described above:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . +CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . +CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_cbcr qp_offset+ . . . +CuQpOffsetJointCbCr).
Video decoder 300 may determine a residual block based on the
quantization parameter. For example, video decoder 300 may
inverse-quantize a plurality of coefficient values based on the
quantization parameter to generate inverse-quantized coefficient
values and inverse-transform the inverse-quantized coefficient
values to generate the residual block. In some examples, such as
transform skip mode, inverse-transform may be skipped.
Video decoder 300 may reconstruct the chroma block based on the
residual block. For example, video decoder 300 may determine a
prediction block for the chroma block and add the residual block to
the prediction block for reconstructing the chroma block.
In the above example, video decoder 300 is described as determining
the block level quantization parameter offset for the chroma block.
However, in some cases, it may be possible that determining block
level quantization parameter offset for a particular chorma block
is disabled. Accordingly, in one or more examples, video decoder
300 may receive a syntax element (e.g., cu_chroma_qp_offset_flag)
indicating that the block level quantization parameter offset is to
be used for determining the block level quantization parameter
offset for the chroma block. In such examples, video decoder 300
may determine the block level quantization parameter offset based
on the syntax element indicating that the block level quantization
parameter offset is to be used (e.g., based on
cu_chroma_qp_offset_flag being true).
In accordance with one or more examples described in this
disclosure, video encoder 200 may be configured to determine a
quantization parameter predictor for a chroma block of video data
based on a quantization parameter for a corresponding luma block.
As one example, the quantization parameter predictor is Qp.sub.Y,
and may be the quantization parameter for a corresponding luma
block or average of plurality of corresponding luma blocks. In some
examples, the quantization parameter predictor may be determined
based on Qp.sub.Y without necessarily being equal to Qp.sub.Y. For
example, the Qp.sub.Y may form as a value into a look up table from
which the quantization parameter predictor is determined. The
quantization parameter predictor may be different for the different
chroma components or may be the same for the different chroma
components.
Video encoder 200 may determine a block level quantization
parameter offset for the chroma block. Examples of the block level
quantization parameter offset include CuQpOffsetCb for the Cb
chroma block, CuQpOffsetCr for the Cr chroma block, and
CuQpOffsetJointCbCr for the JointCbCr chroma block.
Video encoder 200 may construct a list of quantization parameter
offsets (e.g., cb_qp_offset_list, cr_qp_offset_list, and/or
joint_cbcr_qp_offset_list), where the values for the list of
quantization parameter offsets may be pre-stored or signaled. Video
encoder 200 may signal an index into the list of quantization
parameter offsets (e.g., cu_chroma_qp_offset_idx).
In one or more examples, where a first chroma block and a second
chroma block are of the same CU, the index into respective lists of
quantization parameter offsets may be the same. For example,
cu_chroma_qp_offset_idx is the index for both cb_qp_offset_list and
cr_qp_offset_list.
Video encoder 200 may determine a quantization parameter for the
chroma block based on the block level quantization parameter offset
and the quantization parameter predictor. For example, video
encoder 200 may determine at least one of a first quantization
parameter offset for chroma component in a picture parameter set
(e.g., pps_cb_qp_offset for Cb chroma block or pps_cr_qp_offset for
Cr chroma block) or a second quantization parameter offset for
chroma component in a slice parameter set (e.g., slice_cb_qp_offset
for Cb chroma block or slice_cr_qp_offset for Cr chroma block
signaled in slice header).
Video encoder 200 may determine the quantization parameter for the
chroma block by adding the block level quantization parameter
offset and one or both of the first quantization parameter offset
and the second quantization parameter offset. For example, as
described above:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . +CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . +CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_cbcr_qp_offset+ . . . +CuQpOffsetJointCbCr).
Video encoder 200 may quantize coefficient values for a residual
block based on the determined quantization parameter for the chroma
block. For example, video encoder 200 may generate the coefficient
values for the residual block using a tranform (although transform
skip is possible) and quantize coefficient values based on the
quantization parameter to generate quantized coefficient values.
Video encoder 200 may signal information indicative of the
quantized coefficient values.
In the above example, video encoder 200 is described as determining
the block level quantization parameter offset for the chroma block.
However, in some cases, it may be possible that determining block
level quantization parameter offset for a particular chorma block
is disabled. Accordingly, in one or more examples, video encoder
200 may signal a syntax element (e.g., cu_chroma_qp_offset_flag)
indicating that the block level quantization parameter offset is to
be used for determining the block level quantization parameter
offset for the chroma block.
In some examples, video encoder 200 may signal and video decoder
300 may receive CU level chroma delta QP for chroma components. As
one example, video encoder 200 may signal CU level chroma delta QP
for chroma components when dual tree is enabled. In this example, a
chroma delta QP value may be signaled using both absolute value for
chroma delta QP and sign values for chroma delta QP for both Cb and
Cr components. The variables qPi.sub.C, qPi.sub.Cr and qPi.sub.CbCr
can be derived as follows:
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offse-
t+slice_cb_qp_offset+ . . . ChromaCuQpDeltaVal+CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . ChromaCuQpDeltaVal+CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_c bcr_qp_offset+ . . .
ChromaCuQpDeltaVal+CuQpOffsetJointCbCr)
In the above,
ChromaCuQpDeltaVal=chroma_cu_qp_delta_abs*(1-2*chroma_cu_qp_delta_sign_fl-
ag). CuQpOffsetCb=cb_qp_offset_list[cu_chroma_qp_offset_idx] is the
CU level QP offset for Cb and
CuQpOffsetCr=cr_qp_offset_list[cu_chroma_qp_offset_idx] is the CU
level QP offset for Cr, and
CuQpOffsetJointCbCr=joint_cbcr_qp_offset_list[cu_chroma_qp_offset_idx]
is the CU level QP offset for joint CbCr. In this example, video
encoder 200 and video decoder 300 may use both PPS, slice and CU
level QP offsets for chroma when dual tree is enabled.
Partial syntax is as below. <ADD> . . . </ADD> shows
addition and <DELETE> . . . </DELETE> shows
deletion.
TABLE-US-00004 Descriptor transform_unit( x0, y0, tbWidth,
tbHeight, treeType, subTuIndex) { ... <ADD> If(treeType !=
DUAL_TREE_CHROMA) {</ADD> if( ((tu_cbf_luma[ x0 ] [ y0 ] | |
tu_cbf_cb[ x0 ][ y0 ] | | tu_cbf_cr[ x0 ][ y0 ])
<DELETE>&& treeType != DUAL_TREE_CHROMA
</DELETE> && <ADD> treeType != DUAL_TREE_LUMA)
| | (tu_cbf_luma[ x0 ][ y0 ] && treeType ==
DUAL_TREE_LUMA</ADD>)) { if( cu_qp_delta_enabled_flag
&& !IsCuQpDeltaCoded) { cu_qp_delta_abs ae(v) if(
cu_qp_delta_abs) cu_qp_delta_sign_flag ae(v) } } <ADD>} If((
tu_cbf_cb[ x0 ][ y0 ] | | tu_cbf_cr[ x0 ] [ y0 ]) &&
cu_chroma_qp_offset_enabled_flag &&
!IsCuChromaQpOffsetCoded) { cu_chroma_qp_offset_flag ae(v) if(
cu_chroma_qp_offset_flag &&
chroma_qp_offset_list_len_minus1 > 0) cu_chroma_qp_offset_idx
ae(v) if(treeType = = DUAL_TREE_CHROMA &&
cu_chroma_qp_offset_flag) { chroma_cu_qp_delta_abs ae(v) if(
chroma_cu_qp_delta_abs) chroma_cu_qp_delta_sign_flag ae(v) } }
</ADD> ... }
In some examples, video encoder 200 may signal and video decoder
300 may receive chroma delta QPs for chroma components Cb and Cr
and joint_CbCr separately. In one example, in order to provide more
flexible, in the example, the delta QPs for chroma components Cb
and Cr and joint_CbCr are signaled separately. In the example, a
chroma delta QP value is signaled using both absolute value for
chroma delta QP and sign values for chroma delta QP for both Cb and
Cr components. Variables qPi.sub.Cr and qPi.sub.Cr and qPi.sub.CbCr
can be derived as follows:
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . ChromaCuQpDeltaVal)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . ChromaCuQpDeltaVal)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_c bcr_qp_offset+ . . . ChromaCuQpDeltaVal)
Partial syntax is as below. <ADD> . . . </ADD> shows
addition and <DELETE> . . . </DELETE> shows
deletion.
TABLE-US-00005 Descriptor transform_unit( x0, y0, tbWidth,
tbHeight, treeType, subTuIndex) { ... <ADD> If(treeType !=
DUAL_TREE_CHROMA) { </ADD> if( (tu_cbf_luma[ x0 ][ y0 ] | |
tu_cbf_cb[ x0 ][y0 ] | | tu_cbf_cr[ x0 ][ y0 ])
<DELETE>&& treeType != DUAL_TREE_CHROMA
</DELETE> && <ADD> treeType != DUAL_TREE_LUMA)
| | (tu_cbf_luma[ x0 ] [ y0 ] && treeType == DUAL_TREE_LUMA
</ADD>)) { if( cu_qp_delta_enabled_flag &&
!IsCuQpDeltaCoded) { cu_qp_delta_abs ae(v) if( cu_qp_delta_abs)
cu_qp_delta_sign_flag ae(v) } } } <ADD>... if( tu_cbf_cr[ x0
] [ y0 ]) { if( tu_cbf_cb[ x0 ] [ y0 ]) tu_joint_cbcr_residual[ x0
][ y0 ] ae(v) ... If (treeType != DUAL_TREE_LUMA) { if(
chroma_cu_qp_delta_enabled_flag && !IsChromaCuQpDeltaCoded)
{ If (tu_joint_cbcr_residual[x0][y0]) { cbcr_cu_qp_delta_abs ae(v)
if( cbcr_cu_qp_delta_abs) cbcr_cu_qp_delta_sign_flag ae(v) } else {
if(tu_cbf_cb[ x0 ][ y0 ]) { cb_cu_qp_delta_abs ae(v) if(
cb_cu_qp_delta_abs) cb_cu_qp_delta_sign_flag ae(v) } if(tu_cbf_cr[
x0 ] [ y0 ]) { cr_cu_qp_delta_abs ae(v) if( cr_cu_qp_delta_abs)
c_cu_qp_delta_sign_flag ae(v) } } } } } </ADD> ... }
In one example, the condition of signaling the cu level chroma
delta QP and cu level chroma QP offset depends on the CBF flag of
the components. For example, video encoder 200 may only signal
delta QP and/or QP offset when the CBF of corresponding component
is true (e.g. equal to 1).
In one example, if the size of chroma coding block equals to or is
bigger than a predefined size (for example, virtual pipeline data
unit (VPDU) size, or 32.times.32), video encoder 200 may signal the
chroma delta QP and/or chroma QP offset at the first coding block,
no matter the CBF of the first CB is 0 or 1. The specified size can
be predefined in both encoder side and decoder side, or set as a
value signaled from video encoder 200 to video decoder 300 at
sequence level, picture level, slice level. For example, this value
can be signaled in Sequence Parameter Set (SPS), Picture Parameter
Set (PPS), Slice header (SH). In one example, when dual tree is
enabled, video encoder 200 may signal the cu level chroma delta QP
and/or cu level chroma QP offset no matter the cbf of chroma
component is 0 or 1.
FIG. 3 is a block diagram illustrating an example video encoder 200
that may perform the techniques of this disclosure. FIG. 3 is
provided for purposes of explanation and should not be considered
limiting of the techniques as broadly exemplified and described in
this disclosure. For purposes of explanation, this disclosure
describes video encoder 200 in the context of video coding
standards such as the HEVC video coding standard and the H.266
video coding standard in development. However, the techniques of
this disclosure are not limited to these video coding standards,
and are applicable generally to video encoding and decoding.
In the example of FIG. 3, video encoder 200 includes video data
memory 230, mode selection unit 202, residual generation unit 204,
transform processing unit 206, quantization unit 208, inverse
quantization unit 210, inverse transform processing unit 212,
reconstruction unit 214, filter unit 216, decoded picture buffer
(DPB) 218, and entropy encoding unit 220. Any or all of video data
memory 230, mode selection unit 202, residual generation unit 204,
transform processing unit 206, quantization unit 208, inverse
quantization unit 210, inverse transform processing unit 212,
reconstruction unit 214, filter unit 216, DPB 218, and entropy
encoding unit 220 may be implemented in one or more processors or
in processing circuitry. Moreover, video encoder 200 may include
additional or alternative processors or processing circuitry to
perform these and other functions. In other examples, video encoder
200 may include more, fewer, or different units.
Video data memory 230 may store video data to be encoded by the
components of video encoder 200. Video encoder 200 may receive the
video data stored in video data memory 230 from, for example, video
source 104 (FIG. 1). DPB 218 may act as a reference picture memory
that stores reference video data for use in prediction of
subsequent video data by video encoder 200. Video data memory 230
and DPB 218 may be formed by any of a variety of memory devices,
such as dynamic random access memory (DRAM), including synchronous
DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or
other types of memory devices. Video data memory 230 and DPB 218
may be provided by the same memory device or separate memory
devices. In various examples, video data memory 230 may be on-chip
with other components of video encoder 200, as illustrated, or
off-chip relative to those components.
In this disclosure, reference to video data memory 230 should not
be interpreted as being limited to memory internal to video encoder
200, unless specifically described as such, or memory external to
video encoder 200, unless specifically described as such. Rather,
reference to video data memory 230 should be understood as
reference memory that stores video data that video encoder 200
receives for encoding (e.g., video data for a current block that is
to be encoded). Memory 106 of FIG. 1 may also provide temporary
storage of outputs from the various units of video encoder 200.
The various units of FIG. 3 are illustrated to assist with
understanding the operations performed by video encoder 200. The
units may be implemented as fixed-function circuits, programmable
circuits, or a combination thereof. Fixed-function circuits refer
to circuits that provide particular functionality, and are preset
on the operations that can be performed. Programmable circuits
refer to circuits that can be programmed to perform various tasks,
and provide flexible functionality in the operations that can be
performed. For instance, programmable circuits may execute software
or firmware that cause the programmable circuits to operate in the
manner defined by instructions of the software or firmware.
Fixed-function circuits may execute software instructions (e.g., to
receive parameters or output parameters), but the types of
operations that the fixed-function circuits perform are generally
immutable. In some examples, the one or more of the units may be
distinct circuit blocks (fixed-function or programmable), and in
some examples, the one or more units may be integrated
circuits.
Video encoder 200 may include arithmetic logic units (ALUs),
elementary function units (EFUs), digital circuits, analog
circuits, and/or programmable cores, formed from programmable
circuits. In examples where the operations of video encoder 200 are
performed using software executed by the programmable circuits,
memory 106 (FIG. 1) may store the object code of the software that
video encoder 200 receives and executes, or another memory within
video encoder 200 (not shown) may store such instructions.
Video data memory 230 is configured to store received video data.
Video encoder 200 may retrieve a picture of the video data from
video data memory 230 and provide the video data to residual
generation unit 204 and mode selection unit 202. Video data in
video data memory 230 may be raw video data that is to be
encoded.
Mode selection unit 202 includes a motion estimation unit 222,
motion compensation unit 224, and an intra-prediction unit 226.
Mode selection unit 202 may include additional functional units to
perform video prediction in accordance with other prediction modes.
As examples, mode selection unit 202 may include a palette unit, an
intra-block copy unit (which may be part of motion estimation unit
222 and/or motion compensation unit 224), an affine unit, a linear
model (LM) unit, or the like.
Mode selection unit 202 generally coordinates multiple encoding
passes to test combinations of encoding parameters and resulting
rate-distortion values for such combinations. The encoding
parameters may include partitioning of CTUs into CUs, prediction
modes for the CUs, transform types for residual data of the CUs,
quantization parameters for residual data of the CUs, and so on.
Mode selection unit 202 may ultimately select the combination of
encoding parameters having rate-distortion values that are better
than the other tested combinations.
Video encoder 200 may partition a picture retrieved from video data
memory 230 into a series of CTUs, and encapsulate one or more CTUs
within a slice. Mode selection unit 202 may partition a CTU of the
picture in accordance with a tree structure, such as the QTBT
structure or the quad-tree structure of HEVC described above. As
described above, video encoder 200 may form one or more CUs from
partitioning a CTU according to the tree structure. Such a CU may
also be referred to generally as a "video block" or "block."
In general, mode selection unit 202 also controls the components
thereof (e.g., motion estimation unit 222, motion compensation unit
224, and intra-prediction unit 226) to generate a prediction block
for a current block (e.g., a current CU, or in HEVC, the
overlapping portion of a PU and a TU). For inter-prediction of a
current block, motion estimation unit 222 may perform a motion
search to identify one or more closely matching reference blocks in
one or more reference pictures (e.g., one or more previously coded
pictures stored in DPB 218). In particular, motion estimation unit
222 may calculate a value representative of how similar a potential
reference block is to the current block, e.g., according to sum of
absolute difference (SAD), sum of squared differences (SSD), mean
absolute difference (MAD), mean squared differences (MSD), or the
like. Motion estimation unit 222 may generally perform these
calculations using sample-by-sample differences between the current
block and the reference block being considered. Motion estimation
unit 222 may identify a reference block having a lowest value
resulting from these calculations, indicating a reference block
that most closely matches the current block.
Motion estimation unit 222 may form one or more motion vectors
(MVs) that defines the positions of the reference blocks in the
reference pictures relative to the position of the current block in
a current picture. Motion estimation unit 222 may then provide the
motion vectors to motion compensation unit 224. For example, for
uni-directional inter-prediction, motion estimation unit 222 may
provide a single motion vector, whereas for bi-directional
inter-prediction, motion estimation unit 222 may provide two motion
vectors. Motion compensation unit 224 may then generate a
prediction block using the motion vectors. For example, motion
compensation unit 224 may retrieve data of the reference block
using the motion vector. As another example, if the motion vector
has fractional sample precision, motion compensation unit 224 may
interpolate values for the prediction block according to one or
more interpolation filters. Moreover, for bi-directional
inter-prediction, motion compensation unit 224 may retrieve data
for two reference blocks identified by respective motion vectors
and combine the retrieved data, e.g., through sample-by-sample
averaging or weighted averaging.
As another example, for intra-prediction, or intra-prediction
coding, intra-prediction unit 226 may generate the prediction block
from samples neighboring the current block. For example, for
directional modes, intra-prediction unit 226 may generally
mathematically combine values of neighboring samples and populate
these calculated values in the defined direction across the current
block to produce the prediction block. As another example, for DC
mode, intra-prediction unit 226 may calculate an average of the
neighboring samples to the current block and generate the
prediction block to include this resulting average for each sample
of the prediction block.
Mode selection unit 202 provides the prediction block to residual
generation unit 204. Residual generation unit 204 receives a raw,
unencoded version of the current block from video data memory 230
and the prediction block from mode selection unit 202. Residual
generation unit 204 calculates sample-by-sample differences between
the current block and the prediction block. The resulting
sample-by-sample differences define a residual block for the
current block. In some examples, residual generation unit 204 may
also determine differences between sample values in the residual
block to generate a residual block using residual differential
pulse code modulation (RDPCM). In some examples, residual
generation unit 204 may be formed using one or more subtractor
circuits that perform binary subtraction.
In examples where mode selection unit 202 partitions CUs into PUs,
each PU may be associated with a luma prediction unit and
corresponding chroma prediction units. Video encoder 200 and video
decoder 300 may support PUs having various sizes. As indicated
above, the size of a CU may refer to the size of the luma coding
block of the CU and the size of a PU may refer to the size of a
luma prediction unit of the PU. Assuming that the size of a
particular CU is 2N.times.2N, video encoder 200 may support PU
sizes of 2N.times.2N or N.times.N for intra prediction, and
symmetric PU sizes of 2N.times.2N, 2N.times.N, N.times.2N,
N.times.N, or similar for inter prediction. Video encoder 200 and
video decoder 300 may also support asymmetric partitioning for PU
sizes of 2N.times.nU, 2N.times.nD, nL.times.2N, and nR.times.2N for
inter prediction.
In examples where mode selection unit does not further partition a
CU into PUs, each CU may be associated with a luma coding block and
corresponding chroma coding blocks. As above, the size of a CU may
refer to the size of the luma coding block of the CU. The video
encoder 200 and video decoder 300 may support CU sizes of
2N.times.2N, 2N.times.N, or N.times.2N.
For other video coding techniques such as an intra-block copy mode
coding, an affine-mode coding, and linear model (LM) mode coding,
as few examples, mode selection unit 202, via respective units
associated with the coding techniques, generates a prediction block
for the current block being encoded. In some examples, such as
palette mode coding, mode selection unit 202 may not generate a
prediction block, and instead generate syntax elements that
indicate the manner in which to reconstruct the block based on a
selected palette. In such modes, mode selection unit 202 may
provide these syntax elements to entropy encoding unit 220 to be
encoded.
As described above, residual generation unit 204 receives the video
data for the current block and the corresponding prediction block.
Residual generation unit 204 then generates a residual block for
the current block. To generate the residual block, residual
generation unit 204 calculates sample-by-sample differences between
the prediction block and the current block.
Transform processing unit 206 applies one or more transforms to the
residual block to generate a block of transform coefficients
(referred to herein as a "transform coefficient block"). Transform
processing unit 206 may apply various transforms to a residual
block to form the transform coefficient block. For example,
transform processing unit 206 may apply a discrete cosine transform
(DCT), a directional transform, a Karhunen-Loeve transform (KLT),
or a conceptually similar transform to a residual block. In some
examples, transform processing unit 206 may perform multiple
transforms to a residual block, e.g., a primary transform and a
secondary transform, such as a rotational transform. In some
examples, transform processing unit 206 does not apply transforms
to a residual block.
Quantization unit 208 may quantize the transform coefficients in a
transform coefficient block, to produce a quantized transform
coefficient block. Quantization unit 208 may quantize transform
coefficients of a transform coefficient block according to a
quantization parameter (QP) value associated with the current
block. Video encoder 200 (e.g., via mode selection unit 202) may
adjust the degree of quantization applied to the transform
coefficient blocks associated with the current block by adjusting
the QP value associated with the CU. Quantization may introduce
loss of information, and thus, quantized transform coefficients may
have lower precision than the original transform coefficients
produced by transform processing unit 206.
In accordance with one or more examples described in this
disclosure, mode selection unit 202 may be configured to determine
a quantization parameter predictor for a chroma block of the video
data based on a quantization parameter for a corresponding luma
block. For example, mode selection unit 202 may have determined a
quantization parameter for the corresponding luma block or
plurality of corresponding luma blocks, and the quantization
parameter for the corresponding luma block or some average of the
quantization parameters for the plurality of corresponding luma
blocks may form the quantization parameter predictor. The
quantization parameter predictor may be referred to as Qp.sub.Y.
However, in some examples, the quantization parameter predictor may
be determined from the quantization parameter for the corresponding
luma block (e.g., the quantization parameter predictor is
determined from Qp.sub.Y).
Mode selection unit 202 may determine a block level quantization
parameter offset for the chroma block. The chroma block may be Cb
chroma block, Cr chroma block, or a JointCbCr chroma block.
Examples of the block level quantization parameter offsets include
CuOffsetCb for the Cb chroma block, CuOffsetCr for the Cr chroma
block, and CuQpOffsetJointCbCr for the JointCbCr chroma block.
In some examples, mode selection unit 202 may first determine if
block level quantization parameter offset for the particular chroma
block should be enabled. If mode selection unit 202 determines that
block level quantization parameter offset is enabled for the chroma
block, mode selection unit 202 may determine that the
cu_chroma_qp_offset_flag is true, and cause entropy encoding unit
220 to signal information indicating that cu_chroma_qp_offset_flag
is true.
Mode selection unit 202 may construct a list of quantization
parameter offsets. Mode selection unit 202 may determine an index
into the list of quantization parameter offsets for the determined
block level quantization parameter offset. Entropy encoding unit
220 may signal information indicative of the index. Example of the
index includes cu_chroma_qp_off_idx.
Mode selection unit 202 may determine a quantization parameter for
the chroma block based on the block level quantization parameter
offset and the quantization parameter predictor. As one example,
mode selection unit 202 may determine a first quantization
parameter offset (e.g., pps_cb_qp_offset, pps_cr_qp_offset, or
pps_joint_cbcr_qp_offset) in a picture parameter set and a second
quantization parameter offset (e.g., slice_cb_qp_offset,
slice_cr_qp_offset, or slice_joint_cbcr_qp_offset). Mode selection
unit 202 may add the first quantization parameter, second
quantization parameter, and the block level quantization parameter
offset, and clip the result to within a certain range to determine
the quantization parameter for the chroma block.
Quantization unit 208 may quantize coefficient values for a
residual block based on the determined quantization parameter for
the chroma block. Entropy encoding unit 220 may signal information
indicative of the quantized coefficient values.
In the above examples, mode selection unit 202, quantization unit
208, and entropy encoding unit 220 are described as performing the
example techniques. However, any one or combination of components
of video encoder 200 may be configured to perform the example
techniques.
Inverse quantization unit 210 and inverse transform processing unit
212 may apply inverse quantization and inverse transforms to a
quantized transform coefficient block, respectively, to reconstruct
a residual block from the transform coefficient block.
Reconstruction unit 214 may produce a reconstructed block
corresponding to the current block (albeit potentially with some
degree of distortion) based on the reconstructed residual block and
a prediction block generated by mode selection unit 202. For
example, reconstruction unit 214 may add samples of the
reconstructed residual block to corresponding samples from the
prediction block generated by mode selection unit 202 to produce
the reconstructed block.
Filter unit 216 may perform one or more filter operations on
reconstructed blocks. For example, filter unit 216 may perform
deblocking operations to reduce blockiness artifacts along edges of
CUs. Operations of filter unit 216 may be skipped, in some
examples.
Video encoder 200 stores reconstructed blocks in DPB 218. For
instance, in examples where operations of filter unit 216 are not
needed, reconstruction unit 214 may store reconstructed blocks to
DPB 218. In examples where operations of filter unit 216 are
needed, filter unit 216 may store the filtered reconstructed blocks
to DPB 218. Motion estimation unit 222 and motion compensation unit
224 may retrieve a reference picture from DPB 218, formed from the
reconstructed (and potentially filtered) blocks, to inter-predict
blocks of subsequently encoded pictures. In addition,
intra-prediction unit 226 may use reconstructed blocks in DPB 218
of a current picture to intra-predict other blocks in the current
picture.
In general, entropy encoding unit 220 may entropy encode syntax
elements received from other functional components of video encoder
200. For example, entropy encoding unit 220 may entropy encode
quantized transform coefficient blocks from quantization unit 208.
As another example, entropy encoding unit 220 may entropy encode
prediction syntax elements (e.g., motion information for
inter-prediction or intra-mode information for intra-prediction)
from mode selection unit 202. Entropy encoding unit 220 may perform
one or more entropy encoding operations on the syntax elements,
which are another example of video data, to generate
entropy-encoded data. For example, entropy encoding unit 220 may
perform a context-adaptive variable length coding (CAVLC)
operation, a CABAC operation, a variable-to-variable (V2V) length
coding operation, a syntax-based context-adaptive binary arithmetic
coding (SBAC) operation, a Probability Interval Partitioning
Entropy (PIPE) coding operation, an Exponential-Golomb encoding
operation, or another type of entropy encoding operation on the
data. In some examples, entropy encoding unit 220 may operate in
bypass mode where syntax elements are not entropy encoded.
Video encoder 200 may output a bitstream that includes the entropy
encoded syntax elements needed to reconstruct blocks of a slice or
picture. In particular, entropy encoding unit 220 may output the
bitstream.
The operations described above are described with respect to a
block. Such description should be understood as being operations
for a luma coding block and/or chroma coding blocks. As described
above, in some examples, the luma coding block and chroma coding
blocks are luma and chroma components of a CU. In some examples,
the luma coding block and the chroma coding blocks are luma and
chroma components of a PU.
In some examples, operations performed with respect to a luma
coding block need not be repeated for the chroma coding blocks. As
one example, operations to identify a motion vector (MV) and
reference picture for a luma coding block need not be repeated for
identifying a MV and reference picture for the chroma blocks.
Rather, the MV for the luma coding block may be scaled to determine
the MV for the chroma blocks, and the reference picture may be the
same. As another example, the intra-prediction process may be the
same for the luma coding block and the chroma coding blocks.
FIG. 4 is a block diagram illustrating an example video decoder 300
that may perform the techniques of this disclosure. FIG. 4 is
provided for purposes of explanation and is not limiting on the
techniques as broadly exemplified and described in this disclosure.
For purposes of explanation, this disclosure describes video
decoder 300 according to the techniques of VVC and HEVC. However,
the techniques of this disclosure may be performed by video coding
devices that are configured to other video coding standards.
In the example of FIG. 4, video decoder 300 includes coded picture
buffer (CPB) memory 320, entropy decoding unit 302, prediction
processing unit 304, inverse quantization unit 306, inverse
transform processing unit 308, reconstruction unit 310, filter unit
312, and decoded picture buffer (DPB) 314. Any or all of CPB memory
320, entropy decoding unit 302, prediction processing unit 304,
inverse quantization unit 306, inverse transform processing unit
308, reconstruction unit 310, filter unit 312, and DPB 314 may be
implemented in one or more processors or in processing circuitry.
Moreover, video decoder 300 may include additional or alternative
processors or processing circuitry to perform these and other
functions. In other examples, video decoder 300 may include more,
fewer, or different units.
Prediction processing unit 304 includes motion compensation unit
316 and intra-prediction unit 318. Prediction processing unit 304
may include addition units to perform prediction in accordance with
other prediction modes. As examples, prediction processing unit 304
may include a palette unit, an intra-block copy unit (which may
form part of motion compensation unit 316), an affine unit, a
linear model (LM) unit, or the like.
CPB memory 320 may store video data, such as an encoded video
bitstream, to be decoded by the components of video decoder 300.
The video data stored in CPB memory 320 may be obtained, for
example, from computer-readable medium 110 (FIG. 1). CPB memory 320
may include a CPB that stores encoded video data (e.g., syntax
elements) from an encoded video bitstream. Also, CPB memory 320 may
store video data other than syntax elements of a coded picture,
such as temporary data representing outputs from the various units
of video decoder 300. DPB 314 generally stores decoded pictures,
which video decoder 300 may output and/or use as reference video
data when decoding subsequent data or pictures of the encoded video
bitstream. CPB memory 320 and DPB 314 may be formed by any of a
variety of memory devices, such as DRAM, including SDRAM, MRAM,
RRAM, or other types of memory devices. CPB memory 320 and DPB 314
may be provided by the same memory device or separate memory
devices. In various examples, CPB memory 320 may be on-chip with
other components of video decoder 300, or off-chip relative to
those components.
Additionally or alternatively, in some examples, video decoder 300
may retrieve coded video data from memory 120 (FIG. 1). That is,
memory 120 may store data as discussed above with CPB memory 320.
Likewise, memory 120 may store instructions to be executed by video
decoder 300, when some or all of the functionality of video decoder
300 is implemented in software to be executed by processing
circuitry of video decoder 300.
The various units shown in FIG. 4 are illustrated to assist with
understanding the operations performed by video decoder 300. The
units may be implemented as fixed-function circuits, programmable
circuits, or a combination thereof. Similar to FIG. 3,
fixed-function circuits refer to circuits that provide particular
functionality, and are preset on the operations that can be
performed. Programmable circuits refer to circuits that can be
programmed to perform various tasks, and provide flexible
functionality in the operations that can be performed. For
instance, programmable circuits may execute software or firmware
that cause the programmable circuits to operate in the manner
defined by instructions of the software or firmware. Fixed-function
circuits may execute software instructions (e.g., to receive
parameters or output parameters), but the types of operations that
the fixed-function circuits perform are generally immutable. In
some examples, the one or more of the units may be distinct circuit
blocks (fixed-function or programmable), and in some examples, the
one or more units may be integrated circuits.
Video decoder 300 may include ALUs, EFUs, digital circuits, analog
circuits, and/or programmable cores formed from programmable
circuits. In examples where the operations of video decoder 300 are
performed by software executing on the programmable circuits,
on-chip or off-chip memory may store instructions (e.g., object
code) of the software that video decoder 300 receives and
executes.
Entropy decoding unit 302 may receive encoded video data from the
CPB and entropy decode the video data to reproduce syntax elements.
Prediction processing unit 304, inverse quantization unit 306,
inverse transform processing unit 308, reconstruction unit 310, and
filter unit 312 may generate decoded video data based on the syntax
elements extracted from the bitstream.
In general, video decoder 300 reconstructs a picture on a
block-by-block basis. Video decoder 300 may perform a
reconstruction operation on each block individually (where the
block currently being reconstructed, i.e., decoded, may be referred
to as a "current block").
Entropy decoding unit 302 may entropy decode syntax elements
defining quantized transform coefficients of a quantized transform
coefficient block, as well as transform information, such as a
quantization parameter (QP) and/or transform mode indication(s).
Inverse quantization unit 306 may use the QP associated with the
quantized transform coefficient block to determine a degree of
quantization and, likewise, a degree of inverse quantization for
inverse quantization unit 306 to apply. Inverse quantization unit
306 may, for example, perform a bitwise left-shift operation to
inverse quantize the quantized transform coefficients. Inverse
quantization unit 306 may thereby form a transform coefficient
block including transform coefficients.
After inverse quantization unit 306 forms the transform coefficient
block, inverse transform processing unit 308 may apply one or more
inverse transforms to the transform coefficient block to generate a
residual block associated with the current block. For example,
inverse transform processing unit 308 may apply an inverse DCT, an
inverse integer transform, an inverse Karhunen-Loeve transform
(KLT), an inverse rotational transform, an inverse directional
transform, or another inverse transform to the coefficient
block.
Furthermore, prediction processing unit 304 generates a prediction
block according to prediction information syntax elements that were
entropy decoded by entropy decoding unit 302. For example, if the
prediction information syntax elements indicate that the current
block is inter-predicted, motion compensation unit 316 may generate
the prediction block. In this case, the prediction information
syntax elements may indicate a reference picture in DPB 314 from
which to retrieve a reference block, as well as a motion vector
identifying a location of the reference block in the reference
picture relative to the location of the current block in the
current picture. Motion compensation unit 316 may generally perform
the inter-prediction process in a manner that is substantially
similar to that described with respect to motion compensation unit
224 (FIG. 3).
As another example, if the prediction information syntax elements
indicate that the current block is intra-predicted,
intra-prediction unit 318 may generate the prediction block
according to an intra-prediction mode indicated by the prediction
information syntax elements. Again, intra-prediction unit 318 may
generally perform the intra-prediction process in a manner that is
substantially similar to that described with respect to
intra-prediction unit 226 (FIG. 3). Intra-prediction unit 318 may
retrieve data of neighboring samples to the current block from DPB
314.
Reconstruction unit 310 may reconstruct the current block using the
prediction block and the residual block. For example,
reconstruction unit 310 may add samples of the residual block to
corresponding samples of the prediction block to reconstruct the
current block.
Filter unit 312 may perform one or more filter operations on
reconstructed blocks. For example, filter unit 312 may perform
deblocking operations to reduce blockiness artifacts along edges of
the reconstructed blocks. Operations of filter unit 312 are not
necessarily performed in all examples.
Video decoder 300 may store the reconstructed blocks in DPB 314. As
discussed above, DPB 314 may provide reference information, such as
samples of a current picture for intra-prediction and previously
decoded pictures for subsequent motion compensation, to prediction
processing unit 304. Moreover, video decoder 300 may output decoded
pictures from DPB 314 for subsequent presentation on a display
device, such as display device 118 of FIG. 1.
In one or more examples, prediction processing unit 304 and inverse
quantization unit 306, along with reconstruction unit 310 may be
configured to perform one or more example techniques described in
this disclosure. For example, prediction processing unit 304 may
determine a quantization parameter predictor for a chroma block of
the video data based on a quantization parameter for a
corresponding luma block. For example, prediction processing unit
304 may have determined a quantization parameter for the
corresponding luma block or plurality of corresponding luma blocks,
and determined the quantization parameter predictor for the chroma
block based on the quantization parameter for the corresponding
luma block or plurality of corresponding luma blocks. One example
of the quantization parameter predictor is referred to as Qp.sub.Y.
However, in some examples, the quantization parameter predictor may
be determined from the quantization parameter for the corresponding
luma block (e.g., the quantization parameter predictor is
determined from Qp.sub.Y).
Prediction processing unit 304 may determine whether block level
quantization parameter offset is enabled for the chroma block. For
example, prediction processing unit 304 may receive a syntax
element (e.g., cu_chroma_qp_offset_flag) indicating that the block
level quantization parameter offset is to be used for determining
the block level quantization parameter offset for the chroma block.
Prediction processing unit 304 may determine a block level
quantization parameter offset for the chroma block. For example,
prediction processing unit 304 may determine the block level
quantization parameter offset based on the syntax element
indicating that the block level quantization parameter offset is to
be used.
As one example, prediction processing unit 304 may construct a list
of quantization parameter offsets (e.g., cb_qp_offset_list,
cr_qp_offset_list, and/or joint_cbcr_qp_offset_list) and receive an
index (e.g., cu_chroma_qp_offset_idx) into the list of quantization
parameter offsets. Prediction processing unit 304 may determine the
block level quantization parameter offset based on the index into
the list of quantization parameter offsets. Examples of the block
level quantization parameter offset include CuQpOffsetCb,
CuQpOffsetCr, and CuQpOffsetJointCbCr.
The chroma block may be a first chroma block of a first chroma
component (e.g., Cb chroma block) and the list of quantization
parameter offsets may be a first list of quantization parameter
offsets (e.g., cb_qp_offset_list). Prediction processing unit 304
may also construct a list of quantization parameter offsets (e.g.,
cr_qp_offset_list) for a second chroma block of a second chroma
component (e.g., Cr chroma block). In one or more examples,
prediction processing unit 304 may utilize the same index
(cu_chroma_qp_offset_idx) to determine the block level quantization
parameter offset for the first chroma block and to determine the
block level quantization parameter offset for the second chroma
block (e.g., cu_chroma_qp_offset_idx is an index in
cb_qp_offset_list and cr_qp_offset_list).
In one or more examples, the block level quantization parameter
offset may be different for different chroma blocks in the same
picture or slice. For example, the block level quantization
parameter offset may be determined on a chroma block-by-chroma
block basis. For instance, prediction processing unit 304 may
determine the block level quantization parameter for a first chroma
block in a slice or picture, and determine the block level
quantization parameter for a second chroma block in the same slice
or picture, where the two block level quantization parameters may
be different.
Prediction processing unit 304 may determine a quantization
parameter for the chroma block based on the block level
quantization parameter offset and the quantization parameter
predictor. For example, prediction processing unit 304 may receive
at least one of a first quantization parameter offset for chroma
component (e.g., pps_cb_qp_offset, pps_cr_qp_offset, or
pps_joint_cbcr_qp_offset) in a picture parameter set or a second
quantization parameter offset for chroma component (e.g.,
slice_cb_qp_offset, slice_cr_qp_offset, or
slice_joint_cbcr_qp_offset) in a slice parameter set (e.g., slice
header). Prediction processing unit 304 may determine the
quantization parameter for the chroma block based on the block
level quantization parameter offset, at least one of the first
quantization parameter offset or the second quantization parameter
offset, and the quantization parameter predictor.
For example, prediction processing unit 304 may perform the
following operations to determine the block level quantization
parameter offset, examples of which include qPi.sub.Cb, qPi.sub.Cr,
and qPi.sub.CbCr.
qPi.sub.Cb=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cb_qp_offset+slice_cb_-
qp_offset+ . . . +CuQpOffsetCb)
qPi.sub.Cr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_cr_qp_offset+slice_cr_-
qp_offset+ . . . +CuQpOffsetCr)
qPi.sub.CbCr=Clip3(-QpBdOffset.sub.C,69,Qp.sub.Y+pps_joint_cbcr_qp_offset-
+slice_joint_cbcr_qp_offset+ . . . +CuQpOffsetJointCbCr).
Inverse quantization unit 306 and inverse transform processing unit
308 may determine a residual block based on the quantization
parameter. For example, inverse quantization unit 306 may
inverse-quantize (e.g., performing inverse-quantizing) a plurality
of coefficient values based on the quantization parameter to
generate inverse-quantized coefficient values. Inverse transform
processing unit 308 may inverse-transform (e.g., performing
inverse-transforming) the inverse-quantized coefficient values to
generate the generate the residual block.
Reconstruction unit 310 may reconstruct the chroma block based on
the residual block. For example, prediction processing unit 304 may
determine a prediction block for the chroma block. Reconstruction
unit 310 may add the residual block to the prediction block to
reconstruct the chroma block.
FIG. 6 is a flowchart illustrating an example method for encoding a
current block. The current block may comprise a current CU.
Although described with respect to video encoder 200 (FIGS. 1 and
3), it should be understood that other devices may be configured to
perform a method similar to that of FIG. 6. The example techniques
are described with respect to processing circuitry. Examples of the
processing circuitry include the components of video encoder
200.
In one or more examples, memory (e.g., memory 106, video data
memory 230, DPB 218, or some other memory) may be configured to
store a quantization parameter for a corresponding luma block of a
chroma block of the video data. For instance, the processing
circuitry of video encoder 200 may have already determined the
quantization parameter for the corresponding luma block and stored
it in memory. The memory may be coupled to the processing circuitry
of video encoder 200.
The processing circuitry of video encoder 200 may be configured to
determine a quantization parameter predictor for a chroma block of
the video data based on a quantization parameter for a
corresponding luma block (500). For example, the processing
circuitry may utilize the quantization parameter for the
corresponding luma block as an input into a process to determine
the quantization parameter predictor. In some examples, the
quantization parameter predictor may be the quantization parameter
of the corresponding luma block.
The processing circuitry of video encoder 200 may determine a block
level quantization parameter offset for the chroma block (502). In
some examples, the processing circuitry may construct a list of
quantizaton parameter offsets and determine an index into the list
of quantization parameter offsets for the determined block level
quantization parameter offset. The processing circuitry may signal
information indicative of the index.
The processing circuitry of video encoder 200 may determine a
quantization parameter for the chroma block based on the block
level quantization parameter offset and the quantization parameter
predictor (504). In some examples, the processing circuitry may add
the quantization parameter predictor, the block level quantization
parameter offset, a first quantization parameter offset signaled in
the PPS, and a second quantization parameter offset signaled in the
slice parameter set (e.g., slice header) to determine the
quantization parameter for the chroma block.
The processing circuitry may quantize coefficient values for a
residual block based on the determined quantization parameter for
the chroma block (506). The processing circuitry may then signal
information indicative of the quantized coefficient values
(508).
FIG. 7 is a flowchart illustrating an example method for decoding a
current block of video data. The current block may comprise a
current CU. Although described with respect to video decoder 300
(FIGS. 1 and 4), it should be understood that other devices may be
configured to perform a method similar to that of FIG. 7. The
example techniques are described with respect to processing
circuitry. Examples of the processing circuitry include the
components of video decoder 300.
In one or more examples, memory (e.g., memory 120, CPB memory 320,
DPB 314, or some other memory) may be configured to store a
quantization parameter for a corresponding luma block of a chroma
block of the video data. For instance, the processing circuitry of
video decoder 300 may have already determined the quantization
parameter for the corresponding luma block and stored it in memory.
The memory may be coupled to the processing circuitry of video
decoder 300.
The processing circuitry of video decoder 300 may be configured to
determine a quantization parameter predictor for a chroma block of
the video data based on a quantization parameter for a
corresponding luma block (600). For example, the processing
circuitry may utilize the quantization parameter for the
corresponding luma block as an input into a process to determine
the quantization parameter predictor. In some examples, the
quantization parameter predictor may be the quantization parameter
of the corresponding luma block.
The processing circuitry of video decoder 300 may determine a block
level quantization parameter offset for the chroma block (602). In
some examples, the processing circuitry may construct a list of
quantizaton parameter offsets. The processing circuitry may receive
an index into the list of quantization parameter offsets, and
determine the block level quantization parameter offset based on
the received index.
The processing circuitry of video decoder 300 may determine a
quantization parameter for the chroma block based on the block
level quantization parameter offset and the quantization parameter
predictor (604). In some examples, the processing circuitry may add
the quantization parameter predictor, the block level quantization
parameter offset, a first quantization parameter offset received in
the PPS, and a second quantization parameter offset received in the
slice parameter set (e.g., slice header) to determine the
quantization parameter for the chroma block.
The processing circuitry may determine a residual block based on
the quantization parameter (606). For example, the processing
circuitry may inverse-quantize a plurality of coefficient values
based on the quantization parameter to generate inverse-quantized
coefficient values, and inverse-transform the inverse-quantized
coefficient values to generate the residual block. In some
examples, inverse-transform may be skipped, such as for transform
skip mode.
The processing circuitry may reconstruct the chroma block based on
the residual block (608). For example, the processing circuitry may
determine a prediction block for the chroma block and add the
residual block to the prediction block to reconstruct the chroma
block.
It is to be recognized that depending on the example, certain acts
or events of any of the techniques described herein can be
performed in a different sequence, may be added, merged, or left
out altogether (e.g., not all described acts or events are
necessary for the practice of the techniques). Moreover, in certain
examples, acts or events may be performed concurrently, e.g.,
through multi-threaded processing, interrupt processing, or
multiple processors, rather than sequentially.
In one or more examples, the functions described may be implemented
in hardware, software, firmware, or any combination thereof. If
implemented in software, the functions may be stored on or
transmitted over as one or more instructions or code on a
computer-readable medium and executed by a hardware-based
processing unit. Computer-readable media may include
computer-readable storage media, which corresponds to a tangible
medium such as data storage media, or communication media including
any medium that facilitates transfer of a computer program from one
place to another, e.g., according to a communication protocol. In
this manner, computer-readable media generally may correspond to
(1) tangible computer-readable storage media which is
non-transitory or (2) a communication medium such as a signal or
carrier wave. Data storage media may be any available media that
can be accessed by one or more computers or one or more processors
to retrieve instructions, code and/or data structures for
implementation of the techniques described in this disclosure. A
computer program product may include a computer-readable
medium.
By way of example, and not limitation, such computer-readable
storage media can comprise RAM, ROM, EEPROM, CD-ROM or other
optical disk storage, magnetic disk storage, or other magnetic
storage devices, flash memory, or any other medium that can be used
to store desired program code in the form of instructions or data
structures and that can be accessed by a computer. Also, any
connection is properly termed a computer-readable medium. For
example, if instructions are transmitted from a website, server, or
other remote source using a coaxial cable, fiber optic cable,
twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared, radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave are included in
the definition of medium. It should be understood, however, that
computer-readable storage media and data storage media do not
include connections, carrier waves, signals, or other transitory
media, but are instead directed to non-transitory, tangible storage
media. Disk and disc, as used herein, includes compact disc (CD),
laser disc, optical disc, digital versatile disc (DVD), floppy disk
and Blu-ray disc, where disks usually reproduce data magnetically,
while discs reproduce data optically with lasers. Combinations of
the above should also be included within the scope of
computer-readable media.
Instructions may be executed by one or more processors, such as one
or more digital signal processors (DSPs), general purpose
microprocessors, application specific integrated circuits (ASICs),
field programmable gate arrays (FPGAs), or other equivalent
integrated or discrete logic circuitry. Accordingly, the terms
"processor" and "processing circuitry," as used herein may refer to
any of the foregoing structures or any other structure suitable for
implementation of the techniques described herein. In addition, in
some aspects, the functionality described herein may be provided
within dedicated hardware and/or software modules configured for
encoding and decoding, or incorporated in a combined codec. Also,
the techniques could be fully implemented in one or more circuits
or logic elements.
The techniques of this disclosure may be implemented in a wide
variety of devices or apparatuses, including a wireless handset, an
integrated circuit (IC) or a set of ICs (e.g., a chip set). Various
components, modules, or units are described in this disclosure to
emphasize functional aspects of devices configured to perform the
disclosed techniques, but do not necessarily require realization by
different hardware units. Rather, as described above, various units
may be combined in a codec hardware unit or provided by a
collection of interoperative hardware units, including one or more
processors as described above, in conjunction with suitable
software and/or firmware.
Various examples have been described. These and other examples are
within the scope of the following claims.
* * * * *
References